Method of producing roll of optical film laminate with polarizing film

ABSTRACT

A method of producing a roll of an optical film laminate including a polarizing film includes providing a roll of a separator film-attached optical film laminate which includes the steps of: a continuous web of an optical film laminate including a polarizing film which consists of a polyvinyl alcohol type resin layer and has a thickness of 10 μm or less, and a separator film attached to the optical film laminate through an adhesive layer; in a state after the separator film is peeled, detecting a defect existing in the optical film laminate and the adhesive layer; upon detection of a defect in the continuous web of optical film laminate, recording a position of the defect; and winding into a roll a separator film-attached optical film laminate formed by attaching a separator film to the adhesive layer.

TECHNICAL FIELD

The present invention relates to a method of producing a roll of anoptical film laminate with a polarizing film. In particular, the presentinvention relates to a method of producing a roll of an optical filmlaminate including a polarizing film which consists of a polyvinylalcohol type resin with a molecularly oriented dichroic material, andhas a thickness of 10 μm or less.

BACKGROUND ART

There is a widely known method in which a single layer made of apolyvinyl alcohol type resin (hereinafter referred to as “PVA typeresin”) formed in a film shape is subjected to dyeing and stretching toproduce a polarizing film comprising a PVA type resin layer, whereinmolecules of the PVA type resin are oriented in the direction of thestretching, and a dichroic material is absorbed (impregnated) in the PVAtype resin in a molecularly oriented state. The thickness of apolarizing film to be obtained by the above conventional method using aPVA type resin single-layer film is in the range of about 15 to 35 μm.The conventional method makes it possible to obtain a polarizing filmhaving the following optical characteristics of a single layertransmittance of 42% or more and a polarization rate of 99.95% or more.Currently, polarizing films produced by the conventional method are usedin optical display devices for televisions, mobile phones, personaldigital assistants, and other appliances.

However, since the PVA type resins are hydrophilic and highlyhygroscopic, a polarizing film produced using a PVA type resin issensitive to changes in temperature and humidity, and more likely toexpand and contract due to changes in surrounding environments, which isliable to cause the occurrence of crack. Moreover, the expansion andcontraction caused by environmental changes during use will producestress in an adjacent member to which the polarizer film is joined, andthereby cause deformation, such as warp, in the adjacent member.

Thus, in order to suppress expansion and contraction of a polarizer filmto reduce the impact of temperature and humidity, it is usual to employ,as a polarizing film for televisions, a laminate prepared by laminatinga triacetylcellulose (TAC) film having a thickness of 40 to 80 μm andserving as a protection film, on each of opposite surfaces of apolarizing film. However, even in such a structure, in cases where asingle-layer polarizing film is used therein, there is a limit tothinning of the polarizing film. Thus, expansion and contraction forcesof the polarizing film become unignorable, and it is difficult tocompletely suppress the influence of expansion and contraction of thepolarizing film, so that a certain level of expansion and contractionwill inevitably occur in the optical film laminate including thepolarizing film. If expansion or contraction occurs in such an opticalfilm laminate including a polarizing film, stress arising from theexpansion or contraction will cause deformation, such as warp, in anadjacent member. This deformation, even if it is small, leads to theoccurrence of non-uniformity of display in a liquid-crystal displaydevice.

To suppress the occurrence of such non-uniformity of display, designconsiderations should be made to carefully select the material for eachmember to be used in the optical film laminate including the polarizingfilm. Further, the contraction stress of the polarizing film will causepeeling or the like of the optical film laminate from a liquid-crustalpanel. Thus, a high-adhesion adhesive is required to join the opticalfilm laminate to the liquid-crystal display panel. However, the use ofsuch a high-adhesion adhesive gives rise to a problem of difficulty inre-working which is an operation of, when the presence of an opticaldefect is found in a polarizing film of an optical film laminatelaminated to a liquid-crystal display panel through a subsequentinspection, peeling the optical film laminate from the liquid-crystaldisplay panel and laminating another optical film laminate to theliquid-crystal display panel. This is a technical problem in apolarizing film to be obtained by the conventional method using a PVAtype resin single-layer formed in a film shape.

The problem causes a growing demand for a new polarizing film productionmethod, as an alternative to the conventional polarizing film productionmethod using a PVA type resin single-layer, and being incapable ofachieving a sufficient level of thinning of a polarizing film due to theabove problem. Specifically, it is virtually impossible to produce apolarizing film having a thickness of 10 μm or less by the conventionalmethod using a PVA type resin single-layer formed in a film shape. Thisis because, in producing a polarizing film using a film-shaped PVA typeresin single-layer, if the thickness of the PVA type resin single-layeris excessively reduced, dissolution and/or breaking is likely to occurin a PVA type resin layer in a dyeing step and/or a stretching step,which makes it impossible to form a polarizing film having a uniformthickness.

To address the problem, there has been proposed a method designed suchthat a PVA type resin layer is applied and formed on a thermoplasticresin substrate, and the PVA type resin layer formed on the resinsubstrate is stretched together with the resin substrate, and subjectedto dyeing, so as to produce a polarizing film significantly thinner thanthe polarizing film obtained by the conventional method. This polarizingfilm production method using a thermoplastic resin substrate isnoteworthy in that it provides a possibility of producing a polarizingfilm more uniformly than the polarizing film production method using aPVA type resin single-layer.

For example, Japanese Patent JP 4279944B (Patent Document 1) discloses apolarizing plate production method which comprises steps of forming apolyvinyl alcohol resin layer having a thickness of 6 μm to 30 μm, onone of opposite surfaces of a thermoplastic resin film by a coatingprocess, stretching the polyvinyl alcohol resin layer at a stretchingratio of 2.0 to 5.0 in such a manner that the polyvinyl alcohol resinlayer is formed as a transparent coating element layer to thereby form acomposite film consisting of two layers including the thermoplasticresin film and the transparent coating element layer, laminating anoptical transparent resin film layer on the side of the transparentcoating element layer of the composite film consisting of the twolayers, through a bonding agent. peeling and removing the thermoplasticresin film, and dyeing and fixing the transparent coating element layerin such a manner that the transparent coating element layer is formed asa polarizing element layer. A polarizing plate to be obtained by thismethod has a two-layer structure consisting of the optical transparentresin film layer and the polarizing element layer. According to thedescription of the Patent Document 1, the polarizing element has athickness of 2 to 4 μm.

The method disclosed in the Patent Document 1 is designed to perform astretching under an elevated temperature by a uniaxial stretchingprocess, wherein the stretching ratio is restricted to the range of 2.0to 5.0, as mentioned above. As for the reason why the stretching ratiois restricted to 5.0 or less, the Patent Document 1 explains that astretching at a high stretching ratio of greater than 5.0 makes itextremely difficult to maintain stable production. Specifically, thereis described that the ambient temperature during a stretching is set to55° C. in cases where ethylene-vinyl acetate copolymer is used as thethermoplastic resin film, to 60° C. in cases where non-stretchedpolypropylene is used as the thermoplastic resin film, or to 70° C. incases where non-stretched nylon is used as the thermoplastic resin film.The method disclosed in the Patent Document 1 employs a uniaxialstretching process in air under an elevated temperature. Further, asdescribed in the Patent Document 1, the stretching ratio is restrictedto 5.0 or less. Thus, a polarizing film having an extremely smallthickness of 2 to 4 μm, to be obtained by this method, is not enough tosatisfy optical characteristics desired for a polarizing film to beused, for example, in an optical display device such as a liquid-crystaltelevision, or an optical display device using an organic EL displayelement.

The method of forming a polarizing film with steps of forming a PVA typeresin layer on a thermoplastic resin substrate by a coating process, andstretching the PVA type resin layer together with the substrate is alsodisclosed in Japanese Patent Laid-Open Publication JP 2001-343521A(Patent Document 2) and Japanese Patent Laid-Open Publication JP2003-043257A (Patent Document 3). The methods disclosed in the PatentDocuments 2 and 3 are designed such that a laminate consisting of athermoplastic resin substrate and a PVA type resin layer applied on thesubstrate is subjected to a uniaxial stretching at a temperature of 70°C. to 120° C., in cases where the substrate is made of anon-crystallizable polyester resin. Then, the PVA type resin layermolecularly oriented by the stretching is subjected to dyeing to allow adichroic material to be impregnated therein. In the Patent Document 2,there is described that the uniaxial stretching may be a longitudinaluniaxial stretching or may be a transverse uniaxial stretching.Differently, in the Patent Document 3, a method is described in whichthe transverse uniaxial stretching is performed, and, during or afterthe transverse uniaxial stretching, contracting the length in thedirection perpendicular to the direction of the stretching by a specificamount. In both of the Patent Documents 2 and 3, there is described thatthe stretching ratio is typically set to about 4.0 to 8.0. Further,there is described that the thickness of a polarizing film to beobtained is in the range of 1 to 1.6 μm.

In the Patent Documents 2 and 3, although there is described that thestretching ratio is typically set to 4.0 to 8.0, the Patent Documents 2and 3 adopt an elevated temperature in-air stretching process, it isconsidered that the stretching ratio is limited to 5 as described, forexample, in the Patent Document 1. Neither of these describes a specifictechnique for achieving a stretching ratio of greater than 5.0 by theelevated temperature in-air stretching process. In fact, in Examplesdescribed in the Patent Documents 2 and 3, only a stretching ratio of5.0 and a stretching ratio of 4.5 are described, respectively, in thePatent Document 2 and the Patent Document 3. Through additional tests onthe methods disclosed in the Patent Documents 2 and 3, the inventors ofthe present invention have ascertained that it is impossible toadequately perform a stretching at a stretching ratio of greater than5.0 by the methods disclosed therein. Therefore, it should be understoodthat only a stretching ratio of 5.0 or less is substantially disclosedin the Patent Documents 2 and 3. As with the Patent Document 1, thepolarizing film to be obtained by the method disclosed in each of thePatent Documents 2 and 3 is not enough to satisfy opticalcharacteristics desired for a polarizing film to be used, for example,in an optical display device such as a liquid-crystal television.

U.S. Pat. No. 4,659,523 (Patent Document 4) discloses a polarizing filmproduction method which comprises subjecting a PVA type resin layercoated on a polyester film to a uniaxial stretching together with thepolyester film. This method is intended to form the polyester filmserving as a substrate of the PVA type resin layer in such a manner asto have optical characteristics allowing the polyester film to be usedtogether with a polarizing film, but it is not intended to produce apolarizing film comprising a PVA type resin layer and having a smallthickness and excellent optical characteristic. Specifically, the methoddisclosed in the Patent Document 4 is no more than a technique ofimproving optical characteristics of a polyester resin film to bestretched together with a PVA type resin layer to be formed as apolarizing film. A polarizer material production method having the sameobject is also disclosed in Japanese Patent Publication JP 08-012296B(Patent Document 5).

LIST OF PRIOR ART DOCUMENTS Patent Documents

Patent Document 1:Japanese Patent JP 4279944B

Patent Document 2: Japanese Laid-Open Patent Publication JP 2001-343521A

Patent Document 3:Japanese Laid-Open Patent Publication JP 2003-043257A

Patent Document 4:U.S. Pat. No. 4,659,523

Patent Document 5:Japanese Patent Publication JP 08-012296B

Patent Document 6: Japanese Laid-Open Patent Publication JP 2002-258269A

Patent Document 7: Japanese Laid-Open Patent Publication JP 2004-078143A

Patent Document 8: Japanese Laid-Open Patent Publication JP 2007-171892A

Patent Document 9: Japanese Laid-Open Patent Publication JP 2004-338379A

Patent Document 10: Japanese Laid-Open Patent Publication JP2005-248173A

Patent Document 11: Japanese Laid-Open Patent Publication JP2011-002759A

Non-Patent Documents

Non-Patent Document 1: H. W. Siesler, Advanced Polymeric Science, 65, 1,1984

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

As disclosed in the Patent Documents 1 to 5, a method has already beenknown in which a PVA type resin layer is formed on a thermoplastic resinsubstrate by a coating process, and the PVA type resin layer isstretched together with the thermoplastic resin substrate to produce athin polarizing film. However, it has not been realized to obtain ahighly-functional polarizing film usable in a display device satisfyingthe optical characteristics of a contrast ratio of 1000:1 or more, and amaximum luminance (brightness) of 500 cd/m² or more, which are requiredfor a display device, typically, for liquid-crystal televisions, or apolarizing film having optical characteristics usable in an opticaldisplay device using an organic EL display element.

Through extensive effort, the inventors have successfully developed anoptical display device comprising a polarizing film which has asignificantly small thickness as compared with conventional polarizingfilms and exhibits required optical characteristics. It is therefore anobject of the present invention to provide a method of, using the newlydeveloped polarizing film, producing a roll of an optical film laminatewhich is suitable for production of optical display devices.

Means for Solving the Problem

The inventors have successfully obtained a nonconventional polarizingfilm by stretching a non-crystallizable ester type thermoplastic resinsubstrate and a PVA type resin layer applied to and formed on thesubstrate together through a 2-stage stretching step consisting of apreliminary in-air stretching and an in-boric-acid-solution stretching,and subjecting the PVA type resin layer to dyeing with a dichroic dyeingmaterial, wherein the polarizing film has a thickness of 10 μm or less,and optical characteristics of the polarizing film represented by asingle layer transmittance T and a polarization rate P can satisfycharacteristics required for polarizing films for use in optical displaydevices.

The present invention provides a method of producing a roll of anoptical film laminate using such a polarizing film. The method comprisesa step of providing a roll of a separator film-attached optical filmlaminate which comprises a continuous web of an optical film laminateincluding a polarizing film which consists of a polyvinyl alcohol typeresin layer and has a thickness of 10 μm or less and an absorption axisin a lengthwise direction of the optical film laminate, and a separatorfilm attached to the optical film laminate through an adhesive layer,wherein the polarizing film is formed by performing a stretchingsub-step of subjecting a laminate comprising a continuous web of athermoplastic resin substrate and a polyvinyl alcohol type resin layerformed on the substrate, to a uniaxial stretching in a lengthwisedirection of the laminate to attain a stretching ratio of 5.0 to 8.5 tothereby reduce a thickness of the polyvinyl alcohol type resin layer to10 μm or less, and an absorption sub-step of causing a dichroic materialto be absorbed in the polyvinyl alcohol type resin layer, and anadhesion force of the separator film with respect to the adhesive layeris weaker than an adhesion force of the optical film laminate withrespect to the adhesive layer.

The method further comprises the steps of peeling the separator filmfrom the optical film laminate in such a manner as to allow the adhesivelayer to adhere to a side of the polarizing film, while unrolling theoptical film laminate from the roll and feeding the unrolled opticalfilm laminate in the lengthwise direction, in a state after theseparator film is peeled, detecting a defect existing in the opticalfilm laminate and the adhesive layer, upon detection of a defect in thecontinuous web of optical film laminate, recording a position of thedefect, after the step of detecting a defect, attaching a separator filmto the adhesive layer to form a separator film-attached optical filmlaminate, and winding the formed separator film-attached optical filmlaminate.

Preferably, the stretching of the laminate is performed by attain a2-stage stretching consisting of a preliminary in-air stretching and anin-boric-acid-solution stretching, to allow a total stretching ratio tofall within the above range.

The polarizing plate to be used in the present invention has a thicknessof 10 μm or less, i.e., is extremely thin, as set forth above. Thus, inorder to ensure sufficient rigidity during handling, the separator filmis attached to the optical film laminate through the adhesive layer.Further, defect inspection is performed to detect any defect possiblyexisting in the polarizing film. In this case, in order to improveaccuracy of the detection, the defect inspection is performed under acondition that the separator film is peeled from the optical filmlaminate. When the separator is peeled, the adhesive layer is left onthe side of the optical film laminate, because the adhesive layer forbonding the separator film to the optical film laminate has a strongeradhesion force with respect to the optical film laminate than withrespect to the separator film. The adhesive layer will be used asbonding means when the optical film laminate is joined to another membersuch as a display panel in a subsequent step. As above, the separatorfilm is also used as a means to apply the adhesive layer onto theoptical film laminate. In the defect inspection to be performed underthe condition that the separator film is peeled, it is possible todetect a defect possibly existing in the adhesive layer, such as gasbubbles, together with the defect existing in the polarizing film.

In a preferred embodiment, a defect mark can be printed on thecontinuous web of optical film laminate at a position corresponding tothe defect based on the recorded positional information about thedefect. Further, identification information for identifying the opticalfilm laminate having the defect may be stored in an external storagedevice in association with the recorded positional information about thedefect.

In the method of the present invention, the separator film in theseparator film-attached optical film laminate may be attached to theoptical film laminate on the side of the polarizing film. Further, anoptically functional film layer may be disposed between the separatorfilm and the polarizing film. Further, the step of providing a roll of aseparator film-attached optical film laminate may includes steps ofbonding an optically functional film to the continuous web of opticalfilm laminate including the polarizing film, on the side of thepolarizing film, peeling the substrate from the polarizing film, andattaching the separator film to the laminate comprising the polarizingfilm and the optically functional film, on the side of the polarizingfilm, through an adhesive. In this case, before attaching the separatorfilm, a second optically functional film may be bonded to the laminatecomprising the polarizing film and the optically functional film, on theside of the polarizing film, and then the separator film may be attachedonto the second optically functional film through an adhesive.

For characteristics of a polarizing film which is desirable for use inan optical display device such as a liquid-crystal television, theinventors have set conditions represented by the following formulas:

P>−(10^(0929T−42.4)−1)×100 (where T<42.3); and

P≧99.9 (where T>42.3)

wherein T is a single layer transmittance, and P is a polarization rate.

Unlike the liquid-crystal display device, an organic EL display devicetypically uses a single polarizing film. Thus, optical characteristicsrequired for such a polarizing film becomes different from opticalcharacteristics required for the polarizing film for use in theliquid-crystal display device. As for the optical characteristicsrequired for the polarizing film for use in the organic EL displaydevice, the inventers have set conditions represented by the followingformulas:

T≧42.5; and

P≧99.5

wherein T is a single layer transmittance, and P is a polarization rate.

The present invention makes it possible to realize a polarizing filmhaving a thickness of 10 μm or less and exhibiting opticalcharacteristics represented in terms of the single layer transmittanceT, and the polarization rate P satisfying the above conditions. Thepresent invention provides a production method for a roll of an opticalfilm laminate including a polarizing film having such desired opticalcharacteristics.

Effect of the Invention

The present invention makes it possible to obtain a roll of an opticalfilm laminate using a polarizing film which is significantly reduced inthickness as compared to conventional polarizing film while exhibitingrequired optical characteristics, such as a polarizing film whichconsists of a polyvinyl alcohol type resin layer with a molecularlyoriented dichroic material and has a thickness of 10 μm or less andrequired optical characteristics. The present invention also makes itpossible to obtain a roll of an optical film laminate capable ofproviding information about a defect existing in the polarizing film andan adhesive layer.

As mentioned above, any case of using a thermoplastic resin substrateand subjecting a PVA type resin layer formed on the substrate to auniaxial stretching to attain a stretching ratio of 5.0 or more cannotbe found in prior art documents.

A representative example of a polarizing film production method for usein the present invention and an example of an optical film laminate tobe produced by the present invention will be specifically describedbelow with reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an appropriate thickness of a resinsubstrate with respect to a thickness of a PVA type resin layer (or athickness of a polarizing film).

FIG. 2 is a comparative graph illustrating respective polarizationperformances of polarizing films having thicknesses of 3 μm, 8 μm and 10μm.

FIG. 3 is a graph illustrating a relationship between the single layertransmittance T and the polarization rate P.

FIG. 4 is a graph illustrating a range of optical performance requiredfor a polarizing film for use in an optical display device with aliquid-crystal display panel.

FIG. 5 is a graph illustrating theoretical values of polarizationperformances of polarizing films 1 to 7 based on dichroic ratio.

FIG. 6 is a comparative table comparatively illustrating the presence orabsence of dissolution of a PVA type resin layer depending on adifference in iodine concentration of a dyeing bath.

FIG. 7 is a comparative graph illustrating a relationship between aniodine concentration of a dyeing bath and polarization performance of apolarizing film formed by a PVA type resin layer.

FIG. 8 is a graph illustrating respective polarization performances ofpolarizing films in inventive examples.

FIG. 9 is a schematic diagram illustrating a production process forproducing an optical film laminate, wherein the process does not includeany insolubilization treatment.

FIG. 10 is a schematic diagram illustrating a production process forproducing an optical film laminate, wherein the process includes aninsolubilization treatment.

FIG. 11 a is a sectional view illustrating an example of an organic ELdisplay device using an optical film laminate according to the presentinvention.

FIG. 11 b is a sectional view illustrating another example of theorganic EL display device using the optical film laminate according tothe present invention.

FIG. 12 is a sectional view illustrating an example of a liquid-crystaldisplay device using an optical film laminate according to the presentinvention.

FIG. 13 is a graph comparatively illustrating polarization performancesof polarizing films in a group of inventive examples.

FIG. 14 is a graph comparatively illustrating polarization performancesof polarizing films in another group of inventive examples.

FIG. 15 is a graph illustrating polarization performances of polarizingfilms in yet another group of inventive examples.

FIG. 16 is a graph illustrating polarization performances of polarizingfilms in still another group of inventive examples.

FIG. 17 is a graph illustrating polarization performances of polarizingfilms in yet still another group of inventive examples.

FIG. 18 is a graph illustrating a relative relationship between astretching temperature and an attainable stretching ratio in each ofcrystallizable PET, non-crystallizable PET and PVA type resin.

FIG. 19 is a graph illustrating a change in crystallization speed alongwith a change in temperature between a glass transition temperature Tgand a melting point Tm in each of the crystallizable PET and thenon-crystallizable PET.

FIG. 20 is a graph illustrating a relationship between a stretchingratio during an elevated temperature in-air stretching and a totalstretching ratio, in the non-crystallizable PET and the PVA type resin.

FIG. 21 is a graph illustrating a relative relationship between astretching temperature during the elevated temperature in-air stretchingand a total attainable stretching ratio, in each of the crystallizablePET, the non-crystallizable PET and the PVA type resin.

FIG. 22 is a graph illustrating a molecular orientation and a degree ofcrystallization with respect to a total stretching ratio, in PET to beused as a thermoplastic resin substrate.

FIG. 23 is a graph illustrating a relationship between a preliminarystretching temperature during a preliminary in-air stretching at astretching ratio of 1.8, and an orientation function of PET after thepreliminary in-air stretching.

FIG. 24 is a graph illustrating a relationship between a degree ofcrystallization and a orientation function of PVA.

FIG. 25 is a schematic diagram illustrating a production process ofproducing a polarizing film using a thermoplastic resin substrate.

FIG. 26 is a graph illustrating polarization performance of aconventional example of a polarizing film produced without beingsubjected to the 2-stage stretching.

FIG. 27 is a table illustrating conditions for producing a polarizingfilm or an optical film laminate including the polarizing film, in eachExample subjected to the 2-stage stretching.

FIG. 28 is a table illustrating conditions for producing a polarizingfilm or an optical film laminate including the polarizing film, in eachExample subjected to the 2-stage stretching.

FIG. 29 is a comparative table illustrating values of the orientationfunction in Examples subjected to the 2-stage stretching and referencesamples 1 to 3.

FIG. 30 is a schematic diagram illustrating a production process for aroll of an optical film laminate, according to one embodiment of thepresent invention.

FIG. 31 is a schematic diagram illustrating a production process for aroll of an optical film laminate, according to another embodiment of thepresent invention.

FIG. 32 is a schematic diagram illustrating a production process for aroll of an optical film laminate, according to yet another embodiment ofthe present invention.

FIG. 33 is a schematic diagram illustrating a production process for aroll of an optical film laminate, according to still another embodimentof the present invention.

DESCRIPTION OF EMBODIMENTS [Technical Background of Polarizing Films]

As the background art of polarizing films, descriptions will be made onoptical characteristics represented by material characteristics of athermoplastic resin substrate to be used in the present invention andpolarization performance of a polarizing film.

Firstly, descriptions will be made on general material characteristicsof a thermoplastic resin suitable for use in the present invention.

Thermoplastic resins are roughly classified into two types, one beingthe type which is in a state in which polymer molecules are orderlyoriented, and the other being the type which is in a state in whichmolecules are not orderly oriented or only a small portion of polymermolecules are orderly oriented. The former is referred as “crystallizedstate”, and the latter as “amorphous or non-crystallized state.Correspondingly, one type of thermoplastic resin having a propertycapable of being transformed from a non-crystallized state into acrystallized state depending on conditions is called “crystallizableresin”, and the other type of thermoplastic resin which does not havesuch a property is called “non-crystallizable resin”. On the other hand,regardless of whether a crystallizable resin or a non-crystallizableresin, a resin which is not in a crystallized state or has not beentransformed into a crystallized state, is called “amorphous ornon-crystalline resin”. The term “amorphous or non-crystalline” will beused herein in distinction from the term “non-crystallizable” whichmeans a property incapable of transformation into a crystallized state.

For example, the crystallizable resin may include olefin type resinssuch as polyethylene (PE) and polypropylene (PP), and ester type resinssuch as polyethylene terephthalate (PET) and polybutylene terephthalate(PBT). One feature of the crystallizable resin is that, based on heatingand/or stretching/orienting, polymer molecules are orderly arranged, andcrystallization is progressed. Physical properties of the resin varyaccording to the degree of crystallization. On the other hand, even inthe crystallizable resin, such as polypropylene (PP) or polyethyleneterephthalate (PET), it is possible to suppress crystallization byinhibiting polymer molecules from being orderly oriented which mayotherwise be caused by heating or stretching/orienting. Suchcrystallization-inhibited polypropylene (PP) and polyethyleneterephthalate (PET) will hereinafter be referred to respectively as“non-crystallizable polypropylene” and “non-crystallizable polyethyleneterephthalate”, and collectively referred as “non-crystallizable olefintype resin” and “non-crystallizable ester type resin”, respectively.

For example, in the case of polypropylene (PP), the resin may be made tohave an atactic structure having no stereoscopic regularity to therebyproduce a crystallization-inhibited non-crystallizable polypropylene(PP). Further, for example, in the case of polyethylene terephthalate(PET), it is possible to produce a crystallization-inhibitednon-crystallizable polyethylene terephthalate (PET) by copolymerizingisophthalic acid or a modifier group such as 1,4-cyclohexanedimethanol,as a polymerizing monomer, or by copolymerizing a molecule whichinhibits crystallization of polyethylene terephthalate (PET).

Secondly, brief description will be made on optical characteristics of apolarizing film usable in a large-sized liquid-crystal display element.

Basically, the term “optical characteristic” of a polarizing film isused herein to mean a polarization performance represented by apolarization rate P and a single layer transmittance T. In general, thepolarization rate P and the single layer transmittance T of a polarizingfilm are in a trade-off relationship. The two optical characteristicvalues can be expressed by a T-P graph. In the T-P graph, it can beinterpreted that a polarizing film has a better polarizing performanceif a plotted line for the polarizing film is located on a higher side interms of the single layer transmittance and on a higher side in terms ofthe polarization rate in the T-P graph.

Referring to FIG. 3 illustrating such T-P graph, an ideal opticalcharacteristic is a state in which P becomes 100% when T is 50%. As seein FIG. 3, it is easy to increase the value of P in the range where Thas a lower value, and it is difficult to have the P value increased inthe range where T has a higher value. Further, referring to FIG. 4illustrating the polarization performance of a polarizing film based onthe relationship between the transmittance T and the polarization rateP, it is noted that, in a range defined as a region above the line 1 andthe line 2, the single layer transmittance T and the polarization rate Pof the polarizing film have values satisfying the “required performance”which would be required for a liquid-crystal display device, wherein aliquid-crystal display device using this polarizing film will have acontrast ratio of 1000:1 or more, and a maximum luminance of 500 cd/m²or more. This required performance is considered to be opticalcharacteristics required as performance of a polarizing film for alarge-sized liquid-crystal display element or the like, currently oreven in future. An ideal value of the single layer transmittance T is50%. However, when light transmits through a polarizing film, aphenomenon occurs that a part of light is reflected at an interfacebetween the polarizing film and air. Considering this reflectionphenomenon, the single layer transmittance T is reduced by an amountcorresponding to the reflection, and an actually attainable maximumvalue of the single layer transmittance T is in the range of about 45 to46%.

On the other hand, the polarization rate P can be converted to acontrast ratio (CR) of a polarizing film. For example, a polarizationrate P of 99.95% corresponds to a contrast ratio of a polarizing film of2000:1. In a display device prepared by using this polarizing film ineach of opposite sides of a liquid-crystal display panel for aliquid-crystal television, the contrast ratio will be 1050:1. As above,the contrast ratio of the display device is less than that of thepolarizing film, because depolarization occurs within the display panel.The depolarization occurs because of a phenomenon wherein, when lighttransmitted through the polarizing film on a backlight side transmitsthrough the display panel, the light is scattered and/or reflected by apigment in a color filter, a liquid-crystal molecule layer and athin-film transistor (TFT), and so that the polarization state of a partof the light is changed. As the contrast ratio of each of the polarizingfilm and the display panel becomes larger, the liquid-crystal televisionhas better contrast and better visibility.

Meanwhile, the contrast ratio of a polarizing film is defined as a valueobtained by dividing a parallel transmittance (Tp) by a crosstransmittance (Tc). On the other hand, the contrast ratio of a displaydevice is defined as a value obtained by dividing a maximum luminance bya minimum luminance. The minimum luminance is a luminance in a blackscreen. In a liquid-crystal television designed assuming a typicalviewing environment, the minimum luminance is set to 0.5 cd/m² or lessas a reference required value. If the minimum luminance is greater thanthis value, color reproducibility will be deteriorated. The maximumluminance is a luminance in a white screen. In a liquid-crystaltelevision designed for a typical viewing environment, a display havinga maximum luminance ranging from 450 to 550 cd/m² is used. If themaximum luminance is less than this range, visibility of theliquid-crystal television will be decreased because display becomesdark.

Performance required for a display device of a liquid-crystal televisionusing a large-sized display element includes a display contrast ratio of1000:1 or more and a maximum luminance of 500 cd/m² or more. This may beconsidered as a “required performance”. The line 1 (T<42.3%) and theline 2 (T>42.3%) in FIG. 4 denote limit values of the polarizationperformance of a polarizing film necessary to achieve the requiredperformance of the display device. These lines have been determined bythe following simulation, based on a combination of a backlight-sidepolarizing film and a viewing-side polarizing film, illustrated in FIG.5.

The contrast ratio and the maximum luminance of a display device for aliquid-crystal television can be calculated based on a light intensityof a light source (backlight), transmittances of two polarizing filmsdisposed on backlight and viewing sides, a transmittance of aliquid-crystal display panel, polarization rates of the twobacklight-side and viewing-side polarizing films, and a depolarizationrate of the liquid-crystal display panel. The lines 1 and 2 in FIG. 4satisfying the required performance can be derived by preparing aplurality of combinations of two polarizing films different inpolarization performance and calculating a contrast ratio and a maximumluminance of a display device for a liquid-crystal television for eachof the combinations, using basic values of a light intensity (10,000cd/m²) of a light source of a typical liquid-crystal television, atransmittance (13%) of a liquid-crystal display panel of theliquid-crystal television and a depolarization ratio (0.085%) of theliquid-crystal display panel. Specifically, if a polarizing film havingperformance below the line 1 and the line 2 is used, the contrast ratiobecomes less than 1000:1, and the maximum luminance becomes less than500 cd/m2. Formulas used for the calculation are as follows.

Formula (1) is used for deriving the contrast ratio of a display device.Formula (2) is used for deriving the maximum luminance of the displaydevice. Formula (3) is used for deriving a dichroic ratio of apolarizing film.

CRD=Lmax/Lmin,   Formula (1):

Lmax=(LB×Tp−(LB/2×k1B×DP/100)/2×(k1F−k2F))×Tcell/100, and   Formula (2):

DR=A _(k2) /A _(k1)=log(k2)/log(k1)=log(Ts/100×(1−P/100)/T_(PVA))/log(Ts/100×(1+P/100)/T _(PVA)),   Formula (3):

where:

Lmin=(LB×Tc+(LB/2×k1B×DP/100)/2×(k1F−k2F))×Tcell/100;

Tp=(k1B×k1F+k2B×k2F)/2×T _(PVA);

Tc=(k1B×k2F+k2B×k1F)/2×T _(PVA);

k1=Ts/100×(1+P/100)/T _(PVA); and

k2=Ts/100×(1−P/100)/T _(PVA),

wherein:

CRD: contrast ratio of the display device;

Lmax: maximum luminance of the display device;

Lmin: minimum luminance of the display device;

DR: dichroic ratio of the polarizing film;

Ts: single layer transmittance of the polarizing film;

P: polarization rate of the polarizing film;

k1: first primary transmittance;

k2: second primary transmittance;

k1F: k1 of the viewing-side polarizing film;

k2F: k2 of the viewing-side polarizing film;

k1B: k1 of the backlight-side polarizing film;

k2B: k2 of the backlight-side polarizing film;

A_(k1): absorbance of the polarizing film in a direction of atransmission axis;

A_(k2): absorbance of the polarizing film in a direction of anabsorption axis;

LB: light intensity of the light source (10,000 cd/m²);

Tc: cross transmittance of the polarizing films (combination of theviewing-side polarizing film and the backlight-side polarizing film);

Tp: parallel transmittance of the polarizing films (combination of theviewing-side polarizing film and the backlight-side polarizing film);

Tcell: transmittance of the cell (liquid-crystal display panel) (13%);

DP: depolarization rate of the cell (0.085%); and

T_(PVA): transmittance of a PVA film having no iodine absorbed therein(0.92).

The line 1 in FIG. 4 (T<42.3%) is derived based on the polarizationperformance of polarizing films located on the straight line indicated“group 3” in FIG. 5. Among the polarizing films belonging to the group 3in FIG. 5, the polarizing film D which is the plot D (white circle)represented by coordinates (T, P)=(42.1%, 99.95%) may be used on each ofbacklight and viewing sides of a display device for a liquid-crystaltelevision. In this case, the required performance can be satisfied.

On the other hand, although the polarizing film A (T=40.6%, P=99.998%),the polarizing film B (T=41.1%, P=99.994%) and the polarizing film C(T=41.6%, P=99.98%) also belong to the group 3, they are located in aregion having a lower single layer transmittance (darker). Thus, if oneof these polarizing films is used on each of the backlight and viewingsides, the required performance cannot be satisfied. In cases where oneof the polarizing films A, B and C is used on either one of thebacklight and viewing sides, in order to achieve the requiredperformance, it is necessary to use, as a polarizing film to be used onthe other side, a polarizing film having a single layer transmittancegreater than that of the polarizing films in the group 3 and excellentpolarization performance, specifically, at least a polarization rate of99.9% or more, such as the polarizing film E in the group 4, thepolarizing film F in the group 5 or the polarizing film Gin the group 7.

Respective polarization performances of the polarizing films belongingto the groups 1 to 7 are calculated in accordance with the Formula (3).The Formula (3) can be used to calculate the single layer transmittanceT and the polarization rate P based on the dichroic ratio (DR) servingas an index of polarization performance of a polarizing film. The term“dichroic ratio” means a value obtained by dividing an absorbance in adirection of an absorption axis of a polarizing film by an absorbance ina direction of a transmission axis thereof. A higher value of thedichroic ratio indicates better polarization performance. For example,each polarizing film in the group 3 is calculated as a polarizing filmhaving polarization performance in which the dichroic ratio is about 94.This means that any polarizing film having a dichroic ratio of less thanthis value does not achieve the required performance.

Further, in cases where a polarizing film having polarizationperformance inferior to those of the polarizing films in the group 3,such as the polarizing film H (41.0%, 99.95%) in the group 1 or thepolarizing film J (42.0%, 99.9%) in the group 2, is used on either oneof the backlight and viewing sides, in order to achieve the requiredperformance, it is necessary to use, as a polarizing film to be used onthe other side, a polarizing film having polarization performance betterthan those of the polarizing films in the group 3, such as thepolarizing film I (43.2%, 99.95%) in the group 6 or the polarizing filmK (42.0%, 99.998%) in the group 7, as is clear from the Formulas (1) and(2)

In order to achieve the required performance of a display device for aliquid-crystal television, the polarization performance of either one ofthe backlight-side and viewing-side polarizing films has to be betterthan those of the polarizing films in the group 3. The line 1 (T<42.3%)in FIG. 4 indicates the lower limit of the polarization performance. Onthe other hand, the line 2 (T≧42.3%) indicates the lower limit of thepolarization rate P. If a polarizing film having a polarization rate Pof 99.9% or less is used on either one of the backlight and viewingsides, the required performance cannot be satisfied even if a polarizingfilm having the best possible polarization performance is used on theother side.

In conclusion, a desired condition for achieving polarizationperformance required for a display device of a liquid-crystal televisionusing a large-sized display element is that either one of thebacklight-side and viewing-side polarizing films has a polarizationperformance better than that of the polarizing film in a region beyondat least the threshold represented by the line 1 (T<42.3%) and the line2 (T≧42.3%), more specifically, a polarization performance better thanthose of the polarizing films in the group 3, and a polarization rate of99.9% or more.

A polarizing film for use in an organic EL display device is oftenutilized for blocking internally reflected light, in such a manner thatit is combined mainly with a ¼ wavelength phase difference film to formcircularly-polarized light. In this case, a single polarizing film isused. Thus, as mentioned above, optical characteristics required for thepolarizing film to be used in the organic EL display device becomesdifferent from that of the transmissive liquid-crystal display deviceusing two polarizing films. Specifically, it is required to meet theconditions of single layer transmittance T≧42.5, and polarization rateof P≧99.5. The required performance of the polarizing film for use inthe organic EL display device is indicated by the one-dot chain line inFIG. 4.

EXAMPLES ON PRODUCTION OF POLARIZING FILM

Examples 1 to 18 will be described as specific examples of a polarizingfilm for use in an optical film laminate, according to the presentinvention. FIGS. 27 and 28 illustrate conditions for producingpolarizing films in the Examples. Further, for the purpose ofcomparison, reference samples and comparative examples have also beenprepared. FIG. 29 illustrates a value of orientation function of a PETresin substrate of a stretched laminate in each of the Examples 1 to 18and of reference samples 1 to 3, after completion of a first-stageelevated temperature in-air stretching.

Example 1

A continuous web of a substrate was prepared as a non-crystallizableester type thermoplastic resin substrate comprising isophthalicacid-copolymerized polyethylene terephthalate copolymerized with 6 mol %of isophthalic acid (hereinafter referred to as “non-crystallizablePET”). The non-crystallizable PET has a glass transition temperature of75° C. A laminate comprising the continuous web of non-crystallizablePET substrate and a polyvinyl alcohol (hereinafter referred to as “PVA”)layer was prepared in the following manner. By the way, PVA has a glasstransition temperature of 80° C.

A non-crystallizable PET substrate having a thickness of 200 μm wasprepared, and a PVA aqueous solution having a PVA concentration of 4 to5 wt % was also prepared by dissolving a PVA powder having apolymerization degree of 1000 or more and a saponification degree of 99%or more in water. Then, the PVA aqueous solution was applied to the 200mu-thick non-crystallizable PET substrate, and dried at a temperature of50 to 60° C., to form a PVA layer having a thickness of 7 μm on thenon-crystallizable PET substrate. This product will hereinafter bereferred to as a “laminate comprising the non-crystallizable PETsubstrate and the 7 μm-thick PVA layer formed on the non-crystallizablePET substrate”, or as a “laminate including the 7 μm-thick PVA layer”,or simply as a “laminate”.

The laminate including the 7 μm-thick PVA layer was subjected to thefollowing steps including a 2-stage stretching step consisting of apreliminary in-air stretching and an in-boric-acid-solution stretching,to produce a polarizing film having a thickness of 3 μm. Through thefirst-stage preliminary in-air stretching, the laminate including the 7μm-thick PVA layer was stretched together with the non-crystallizablePET substrate to form a stretched laminate including a 5 μm-thick PVAlayer. This product will hereinafter be referred to as a “stretchedlaminate”. Specifically, the stretched laminate was obtained by placingthe laminate including the 7 μm-thick PVA layer into a stretchingapparatus arranged in an oven set to a stretching temperatureenvironment of 130° C., to stretch the laminate in an end-free uniaxialmanner to attain a stretching ratio of 1.8. Through this stretchingstep, the PVA layer in the stretched laminate was converted into a 5μm-thick PVA layer in which PVA molecules are oriented.

Subsequently, the stretched laminate was subjected to a dyeing step toform a dyed laminate in which iodine is absorbed (impregnated) in the 5μm-thick PVA layer having the oriented PVA molecules. This product willhereinafter be referred to as a “dyed laminate”. Specifically, the dyedlaminate was obtained by immersing the stretched laminate in a dyeingsolution having a temperature of 30° C. and containing iodine andpotassium iodide, for an arbitrary time, to cause iodine to be absorbedin the PVA layer included in the stretched laminate, so as to allow thePVA layer for making up a target polarizing film (to a polarizing filmto be finally formed) to have a single layer transmittance of 40 to 44%.In this step, the dyeing solution was prepared by adjusting aconcentration of iodine and a concentration of potassium iodide to fallwithin the range of 0.12 to 0.30 wt % and the range of 0.7 to 2.1 wt %,respectively, using water as a solvent. A ratio of the concentration ofiodine to the concentration of potassium iodide is 1:7.

By the way, it is necessary to use potassium iodide to allow iodine tobe dissolved in water. More specifically, the stretched laminate wasimmersed in a dyeing solution having an iodine concentration of 0.30 wt% and a potassium iodide concentration of 2.1 wt %, for 60 seconds, toform a dyed laminate in which iodine is absorbed in the 5 μm-thick PVAlayer having the oriented PVA molecules. In the Example 1, various dyedlaminates different in single layer transmittance and polarization ratewere formed by changing an immersion time of the stretched laminate inthe dyeing solution having an iodine concentration of 0.30 wt % and apotassium iodide concentration of 2.1 wt %, to adjust an amount ofiodine to be absorbed, so as to allow a target polarizing film to have asingle layer transmittance of 40 to 44%.

Further, through the second-stage in-boric-acid-solution stretching, thedyed laminate was further stretched together with the non-crystallizablePET substrate to form an optical film laminate including a PVA layermaking up a 3 μm-thick polarizing film. This product will hereinafter bereferred to as an “optical film laminate”. Specifically, the opticalfilm laminate was obtained by feeding the dyed laminate through astretching apparatus arranged in treatment equipment having a boric acidaqueous solution containing boric acid and potassium iodide and having atemperature of 60 to 85° C., to subject the dyed laminate to an end-freeuniaxial stretching to attain a stretching ratio of 3.3. Morespecifically, the temperature of the boric acid aqueous solution was 65°C. Further, the boric acid aqueous solution was set to contain 4 weightparts of boric acid with respect to 100 weight parts of water, and 5weight parts of potassium iodide with respect to 100 weight parts ofwater.

In this step, the dyed laminate having iodine impregnated therein in anadjusted amount was first immersed in the boric acid aqueous solutionfor 5 to 10 seconds. Then, the dyed laminate was fed to directly passbetween each of a plurality of set of rolls having differentcircumferential speeds and serving as the stretching apparatus arrangedin the treatment equipment, and subjected to an end-free uniaxialstretching to attain a stretching ratio of 3.3 by taking a time of 30 to90 seconds. Through this stretching, the PVA layer included in the dyedlaminate is changed into a 3 μm-thick PVA layer in which absorbed iodineis highly oriented in one direction in the form of a polyiodide ioncomplex. This PVA layer makes up a polarizing film of an optical filmlaminate.

As above, in the Example 1, a laminate comprising a non-crystallizablePET substrate and a 7 μm-thick PVA layer formed on the substrate isfirst subjected to a preliminarily in-air stretching at a stretchingtemperature of 130° C. to form a stretched laminate. Then, the stretchedlaminate is subjected to dyeing to form a dyed laminate. Then, the dyedlaminate is subjected to an in-boric-acid-solution stretching at astretching temperature of 65° C., to form an optical film laminateincluding a 3 μm-thick PVA layer stretched together with thenon-crystallizable PET substrate to attain a total stretching ratio of5.94. Through the 2-stage stretching, it becomes possible to form anoptical film laminate including a 3 μm-thick PVA layer in which PVAmolecules in the PVA layer formed on the non-crystallizable PETsubstrate are highly oriented, and iodine absorbed through the dyeing ishighly oriented in one direction in the form of a polyiodide ioncomplex.

Then, in a cleaning step although it is not essential in a productionprocess of an optical film laminate, the optical film laminate was takenout of the boric acid aqueous solution, and boric acid deposited on asurface of the 3 μm-thick PVA layer formed on the non-crystallizable PETsubstrate was cleaned by a potassium iodide aqueous solution.Subsequently, in a drying step, the cleaned optical film laminate wasdried by warm air at a temperature of 60° C. The cleaning step isdesigned to solve defective appearance due to deposition of boric acid.

Subsequently, in a lamination and/or transfer step, an 80 μm-thicktriacetylcellulose

(TAC) film was laminated to a surface of the 3 μm-thick PVA layer formedon the non-crystallizable PET substrate, while applying a bonding agentonto the surface of the 3 μm-thick PVA layer. Then, thenon-crystallizable PET substrate was peeled to allow the 3 μm-thick PVAlayer to be transferred to the 80 μm-thick triacetylcellulose (TAC)film.

Example 2

In the Example 2, as with the Example 1, a 7 μm-thick PVA layer wasformed on a non-crystallizable PET substrate to form a laminate, andthen the laminate including the 7 μm-thick PVA layer was subjected to apreliminary in-air stretching and stretched at a stretching ratio of 1.8to form a stretched laminate, whereafter the stretched laminate wasimmersed in a dyeing solution containing iodine and potassium iodide andhaving a temperature of 30° C. to form a dyed laminate including aniodine-absorbed PVA layer. Differently from the Example 1, a process inthe Example 2 additionally comprises a cross-linking step. Thecross-linking step is designed to immerse the dyed laminate in across-linking boric acid aqueous solution at a temperature of 40° C.,for 60 seconds, so as to allow PVA molecules of the iodine-absorbed PVAlayer to be subjected to cross-linking. The cross-linking boric acidaqueous solution in this step was set to contain 3 weight parts of boricacid with respect to 100 weight parts of water, and 3 weight parts ofpotassium iodide with respect to 100 weight parts of water.

The cross-linking step in the Example 2 is intended to expect at leastthree technical effects. The first is an insolubilization effect ofpreventing a thinned PVA layer included in the dyed laminate from beingdissolved during a subsequent in-boric-acid-solution stretching. Thesecond is a dyeing stabilization effect of preventing elution of iodineabsorbed in the PVA layer. The third is a node formation effect offorming nodes by cross-linking molecules of the PVA layer together.

In the Example 2, the cross-linked dyed laminate was immersed in anin-boric-acid-solution stretching bath at 75° C. which is higher than astretching temperature of 65° C. in the Example 1, and stretched at astretching ratio of 3.3 to form an optical film laminate, as with theExample 1. The process in the Example 2 further comprises a cleaningstep, a drying step and a lamination and/or transfer step each of whichis the same as that in the Example 1.

In order to further clarify the technical effects expected of thecross-linking step in advance of the in-boric-acid-solution stretching,a non-cross-linked dyed laminate in the Example 1 was immersed in thein-boric-acid-solution stretching bath at a stretching temperature of 70to 75° C. In this case, the PVA layer included in the dyed laminate wasdissolved in the in-boric-acid-solution stretching bath to preclude thestretching.

Example 3

In the Example 3, as with the Example 1, a 7 μm-thick PVA layer wasformed on a non-crystallizable PET substrate to form a laminate, andthen the laminate including the 7 μm-thick PVA layer was subjected to apreliminary in-air stretching and stretched at a stretching ratio of 1.8to form a stretched laminate. Differently from the Example 1, a processin the Example 3 additionally comprises an insolubilization step. Theinsolubilization step is designed to immerse the stretched laminate in aboric acid insolubilizing aqueous solution at a solution temperature of30° C., for 30 seconds, so as to insolubilize a PVA layer included inthe stretched laminate and having oriented PVA molecules. The boric acidinsolubilizing aqueous solution in this step was set to contain 3 weightparts of boric acid with respect to 100 weight parts of water. Atechnical effect expected of the insolubilization step in the Example 3is to prevent the PVA layer included in the stretched laminate frombeing dissolved at least during a subsequent dyeing step.

In the Example 3, as with the Example 1, the insolubilized stretchedlaminate was immersed in a dyeing solution containing iodine andpotassium iodide and having a temperature of 30° C. to form a dyedlaminate including an iodine-absorbed PVA layer. Subsequently, the dyedlaminate was immersed in the in-boric-acid-solution stretching bath at65° C. which is equal to the stretching temperature in the Example 1,and stretched at a stretching ratio of 3.3 in the same manner as that inthe Example 1 to form an optical film laminate. The process in theExample 3 further comprises a cleaning step, a drying step and alamination and/or transfer step each of which is the same as that in theExample 1.

In order to further clarify the technical effects expected of theinsolubilization step in advance of the dyeing step, a non-insolubilizedstretched laminate in the Example 1 was subjected to dyeing to form adyed laminate, and the formed dyed laminate was immersed in thein-boric-acid-solution stretching bath at a stretching temperature of 70to 75° C. In this case, the PVA layer included in the dyed laminate wasdissolved in the in-boric-acid-solution stretching bath to preclude thestretching, as with the Example 2.

In another test, in place of the dyeing solution in the Example 1 wherea concentration of iodine is set to 0.30 wt % using water as a solvent,a dyeing solution was prepared to set an iodine concentration in therange of 0.12 to 0.25 wt %, while keeping the remaining conditionsunchanged. Then, the non-insolubilized stretched laminate in the Example1 was immersed in the prepared dyeing solution. In this case, the PVAlayer included in the stretched laminate was dissolved in the dyeingbath to preclude the dyeing. In contrast, when the insolubilizedstretched laminate in the Example 3 was used, the dyeing to the PVAlayer could be performed without dissolution of the PVA layer, even ifthe iodine concentration of the dyeing solution was in the range of 0.12to 0.25 wt %.

In the Example 3 where the dyeing to the PVA layer can be performed evenif the iodine concentration of the dyeing solution is in the range of0.12 to 0.25 wt %, various dyed laminates different in single layertransmittance and polarization rate were formed by changing the iodineconcentration and the potassium iodide concentration of the dyeingsolution in the certain range in the Example 1, while keeping animmersion time of the stretched laminate in the dyeing solutionconstant, to adjust an amount of iodine to be absorbed, so as to allow atarget polarizing film to have a single layer transmittance of 40 to44%.

Example 4

In the Example 4, an optical film laminate was formed by a productionprocess in which the insolubilization step in the Example 3 and thecross-linking step in the Example 2 are added to the production processin the Example 1. Firstly, a 7 μm-thick PVA layer was formed on anon-crystallizable PET substrate to form a laminate, and then thelaminate including the 7 μm-thick PVA layer was subjected to apreliminary in-air stretching based on an end-free uniaxial stretchingprocess to attain a stretching ratio of 1.8 to thereby form a stretchedlaminate. In the Example 4, as with the Example 3, through theinsolubilization step of immersing the formed stretched laminate in aboric acid insolubilizing solution at a temperature of 30° C. for 30seconds, the PVA layer included in the stretched laminate and havingoriented PVA molecules was insolubilized. Then, in the Example 4, aswith the Example 3, the stretched laminate including the insolubilizedPVA layer was immersed in a dyeing solution containing iodine andpotassium iodide and having a temperature of 30° C. to form a dyedlaminate including an iodine-absorbed PVA layer.

In the Example 4, as with the Example 2, through the cross-linking stepof immersing the formed dyed laminate in a boric acid cross-linkingsolution at 40° C. for 60 seconds, PVA molecules of the iodine-absorbedPVA layer are cross-linked together. Then, in the Example 4, thecross-linked dyed laminate was immersed in an in-boric-acid-solutionstretching bath at 75° C. which is higher than a stretching temperatureof 65° C. in the Example 1, for 5 to 10 seconds, and subjected to anend-free uniaxial stretching to attain a stretching ratio of 3.3, in thesame manner as that in the Example 2, to thereby form an optical filmlaminate. The process in the Example 4 further comprises a cleaningstep, a drying step and a lamination and/or transfer step each of whichis the same as that in each of the Examples 1 to 3.

As with the Example 3, the PVA layer in the Example 4 is never dissolvedeven if the iodine concentration of the dyeing solution is in the rangeof 0.12 to 0.25 wt %. In the Example 4, various dyed laminates differentin single layer transmittance and polarization rate were formed bychanging the iodine concentration and the potassium iodide concentrationof the dyeing solution in the certain range in the Example 1, whilekeeping an immersion time of the stretched laminate in the dyeingsolution constant, to adjust an amount of iodine to be absorbed, so asto allow a target polarizing film to have a single layer transmittanceof 40 to 44%.

As above, in the Example 4, a 7 μm-thick PVA layer is formed on anon-crystallizable PET substrate to form a laminate, and then thelaminate including the 7 μm-thick PVA layer is subjected to apreliminarily in-air stretching based on an end-free uniaxial stretchingprocess to attain a stretching ratio of 1.8 to thereby form a stretchedlaminate. The formed stretched laminate is immersed in a boric acidinsolubilizing solution at a solution temperature of 30° C. for 30seconds to insolubilize the PVA layer included in the stretchedlaminate. The stretched laminate including the insolubilized PVA layeris immersed in a dyeing solution containing iodine and potassium iodideand having a temperature of 30° C. to form a dyed laminate in whichiodine is absorbed in the insolubilized PVA layer. The dyed laminateincluding the iodine-absorbed PVA layer is immersed in a boric acidcross-linking solution at 40° C. for 60 seconds to cross-link PVAmolecules of the iodine-absorbed PVA layer together. The dyed laminateincluding the cross-linked PVA layer is immersed in anin-boric-acid-solution stretching bath containing iodine and potassiumiodide and having a temperature of 75° C., for 5 to 10 seconds, and thensubjected to an in-boric-acid-solution stretching based on an end-freeuniaxial stretching process to attain a stretching ratio of 3.3 tothereby form an optical film laminate.

In the Example 4, based on the 2-stage stretching consisting of theelevated temperature in-air stretching and the in-boric-acid-solutionstretching, and pre-treatments consisting of the insolubilization inadvance of the immersion into a dyeing bath and the cross-linking inadvance of the in-boric-acid-solution stretching, it becomes possible tostably form an optical film laminate including a 3 μm-thick PVA layermaking up a polarizing film, in which PVA molecules of the PVA layerformed on the non-crystallizable PET substrate are highly oriented, andiodine reliably absorbed in the PVA molecules through the dyeing ishighly oriented in one direction in the form of a polyiodide ioncomplex.

Example 5

In the Example 5, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is a thickness of the PVA layer formed on thenon-crystallizable PET substrate. In the Example 4, the PVA layerinitially had a thickness of 7 μm, and the PVA layer finally included inthe optical film laminate had a thickness of 3 μm, whereas, in theExample 5, the PVA layer initially had a thickness of 12 μm, and the PVAlayer finally included in the optical film laminate had a thickness of 5μm.

Example 6

In the Example 6, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is a polymerizing monomer used in the non-crystallizablePET substrate. In the Example 4, the non-crystallizable PET substratewas prepared by copolymerizing PET and isophthalic acid, whereas, in theExample 6, the non-crystallizable PET substrate was prepared bycopolymerizing PET and 1,4-cyclohexanedimethanol serving as a modifiergroup.

Example 7

In the Example 7, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that a stretching ratio for each of the preliminaryin-air stretching and the in-boric-acid-solution stretching was changedto allow a total stretching ratio to become equal to or close to 6.0. Inthe Example 4, the stretching ratios for the preliminary in-airstretching and the in-boric-acid-solution stretching were set,respectively, to 1.8 and 3.3, whereas, in the Example 7, the twostretching ratios were set, respectively, to 1.2 and 4.9. Meanwhile, thetotal stretching ratio in the Example 4 was 5.94, whereas the totalstretching ratio in the Example 7 was 5.88. The reason is that, in thein-boric-acid-solution stretching, it was unable to perform thestretching at a stretching ratio of 4.9 or more.

Example 8

In the Example 8, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that a stretching ratio for each of the preliminaryin-air stretching and the in-boric-acid-solution stretching was changedto allow a total stretching ratio to become equal to 6.0. In the Example8, the stretching ratios for the preliminary in-air stretching and thein-boric-acid-solution stretching were set to 1.5 and 4.0, respectively.

Example 9

In the Example 9, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that a stretching ratio for each of the preliminaryin-air stretching and the in-boric-acid-solution stretching was changedto allow a total stretching ratio to become equal to 6.0. In the Example9, the stretching ratios for the preliminary in-air stretching and thein-boric-acid-solution stretching were set to 2.5 and 2.4, respectively.

Example 10

In the Example 10, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.In the Example 4, a stretching temperature for the preliminary in-airstretching was set to 130° C., whereas, in the Example 10, thestretching temperature for the preliminary in-air stretching was set to95° C.

Example 11

In the Example 11, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.In the Example 4, the stretching temperature for the preliminary in-airstretching was set to 130° C., whereas, in the Example 11, thestretching temperature for the preliminary in-air stretching was set to110° C.

Example 12

In the Example 12, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.In the Example 4, the stretching temperature for the preliminary in-airstretching was set to 130° C., whereas, in the Example 12, thestretching temperature for the preliminary in-air stretching was set to150° C.

Example 13

In the Example 13, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that the stretching ratio for the preliminary in-airstretching was set to 1.8, and the stretching ratio for thein-boric-acid-solution stretching was changed to 2.8. As a result, inthe Example 13, the total stretching ratio was about 5.0 (accurately,5.04), whereas, in the Example 4, the total stretching ratio was about6.0 (accurately, 5.94).

Example 14

In the Example 14, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that the stretching ratio for the preliminary in-airstretching was set to 1.8, and the stretching ratio for thein-boric-acid-solution stretching was changed to 3.1. As a result, inthe Example 14, the total stretching ratio was about 5.5 (accurately,5.58), whereas, in the Example 4, the total stretching ratio was about6.0 (accurately, 5.94).

Example 15

In the Example 15, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is that the stretching ratio for the preliminary in-airstretching was set to 1.8, and the stretching ratio for thein-boric-acid-solution stretching was changed to 3.6. As a result, inthe Example 15, the total stretching ratio was about 6.5 (accurately,6.48), whereas, in the Example 4, the total stretching ratio was about6.0 (accurately, 5.94).

Example 16

In the Example 16, an optical film laminate was produced under the sameconditions as those in the Example 4, except the following difference.The difference is a stretching scheme in the preliminary in-airstretching. In the Example 4, the preliminary in-air stretching wasperformed based on an end-free uniaxial stretching process to attain astretching ratio of 1.8, whereas, in the Example 16, the preliminaryin-air stretching was performed based on an end-fixed uniaxialstretching process to attain a stretching ratio of 1.8.

Example 17

In the Example 17, an optical film laminate was produced under the sameconditions as those in the Example 16, except the following difference.The difference is that the stretching ratio for the preliminary in-airstretching was set to 1.8, and the stretching ratio for thein-boric-acid-solution stretching was changed to 3.9. As a result, inthe Example 17, the total stretching ratio was about 7.0 (accurately,7.02), whereas, in the Example 16, the total stretching ratio was about6.0 (accurately, 5.94).

Example 18

In the Example 18, an optical film laminate was produced under the sameconditions as those in the Example 16, except the following difference.The difference is that the stretching ratio for the preliminary in-airstretching was set to 1.8, and the stretching ratio for thein-boric-acid-solution stretching was changed to 4.4. As a result, inthe Example 18, the total stretching ratio was about 8.0 (accurately,7.92), whereas, in the Example 16, the total stretching ratio was about6.0 (accurately, 5.94).

Comparative Example 1

The comparative example 1 has been prepared, under the same conditionsas those in the Example 4, by applying a PVA solution to a 200 μm-thicknon-crystallizable PET substrate, and drying to form a laminatecomprising the non-crystallizable PET substrate and a 7 μm-thick PVAlayer formed on the substrate. Then, the laminate including the 7μm-thick PVA layer was subjected to an elevated temperature in-airstretching at a stretching temperature of 130° C. based on an end-freeuniaxial stretching process to attain a stretching ratio of 4.0 tothereby form a stretched laminate. Through the stretching, the PVA layerincluded in the stretched laminate was changed to a 3.5 μm-thick PVAlayer having oriented PVA molecules.

Then, the stretched laminate was subjected to dyeing to form a dyedlaminate in which iodine is absorbed in the 3.5 μm-thick PVA layerhaving the oriented PVA molecules. Specifically, the dyed laminate wasobtained by immersing the stretched laminate in a dyeing solution havinga temperature of 30° C. and containing iodine and potassium iodide, foran arbitrary time, to cause iodine to be absorbed in the PVA layerincluded in the stretched laminate, so as to allow the PVA layer formaking up a target polarizing film to have a single layer transmittanceof 40 to 44%. Various dyed laminates different in single layertransmittance and polarization rate were formed by adjusting an amountof iodine to be absorbed in the PVA layer having the oriented PVAmolecules, in the above manner.

Further, the dyed laminated was subjected to cross-linking.Specifically, the dyed laminated was cross-linked in such a manner thatit is immersed in a boric acid cross-linking solution containing 3weight parts of boric acid with respect to 100 weight pars of water and3 weight parts of potassium iodide with respect to 100 weight pars ofwater and having a temperature of 40° C., for 60 seconds. Thecross-linked dyed laminate in the comparative example 1 corresponds tothe optical film laminate in the Example 4. Thus, a cleaning step, adrying step and a lamination and/or transfer step in the comparativeexample 1 are the same as those in the Example 4.

Comparative Example 2

In the comparative example 2, the laminates in accordance with thecomparative example 1 have been stretched to the stretching ratio of4.5, 5.0 and 6.0, respectively. The following comparative tableillustrates phenomena in a 200 μm-thick non-crystallizable PET substrateand a PVA layer formed on the non-crystallizable PET substrate,including the comparative examples 1 and 2. Based on the data, it hasbeen verified that the stretching ratio during the elevated temperaturein-air stretching at a stretching temperature of 130° C. has an upperlimit of 4.0.

[Technical Background Relating to Stretching]

FIGS. 18 to 22 show results derived from experimental tests. Referringfirst to FIG. 18, FIG. 18 is a graph illustrating a relativerelationship between the stretching temperature and the attainablestretching ratio in each of a crystallizable PET, a non-crystallizablePET and a PVA type resin, based on experimental tests.

In FIG. 18, the thick solid line indicates a change in attainablestretching ratio in a non-crystallizable PET along with a change instretching temperature. The non-crystallizable PET has a glasstransition temperature Tg of about 75° C., and cannot be stretched at atemperature below this glass transition temperature Tg. As is evidentfrom FIG. 18, an end-free uniaxial stretching process to be performed inair under an elevated temperature (elevated temperature in-air end-freeuniaxial stretching) is capable of achieving a stretching ratio of 7.0or more under a stretching temperature of about 110° C. or more. On theother hand, the thin solid line in FIG. 18 indicates a change inattainable stretching ratio in a crystallizable PET along with a changein stretching temperature. The crystallizable PET has a glass transitiontemperature Tg of about 80° C., and cannot be stretched under atemperature below this glass transition temperature Tg.

FIG. 19 illustrates a change in crystallization speed in each of thecrystallizable PET and the non-crystallizable PET along with a change intemperature between a glass transition temperature Tg and a meltingpoint Tm of polyethylene terephthalate (PET). FIG. 19 shows that thecrystallizable PET in an amorphous state at a temperature of about 80 to110° C. is rapidly crystallized at about 120° C.

As is clear from FIG. 18, in the crystallizable PET, an attainablestretching ratio during the elevated temperature in-air end-freeuniaxial stretching has an upper limit of 4.5 to 5.5. In addition, anapplicable stretching temperature is extremely limited, specifically, inthe range of about 90° C. to about 110° C.

FIG. 29 illustrates an example where the elevated temperature in-airend-free uniaxial stretching is performed using a crystallizable PET, asthe reference samples 1 to 3. In each of the reference samples, a 3.3μm-thick polarizing film was produced by forming a 7 μm-thick PVA layeron a 200 μm-thick crystallizable PET substrate to form a laminate, andstretching the laminate in air under elevated temperature. There is adifference between stretching temperatures of the reference samples.Specifically, the stretching temperatures are 110° C. in the referencesample 1, 100° C. in the reference sample 2 and 90° C. in the referencesample 3. A noteworthy parameter is an attainable stretching ratio. Anupper limit of the attainable stretching ratio in the reference sample 1is 4.0, and an upper limit of the attainable stretching ratio in each ofthe reference samples 2 and 3 is 4.5. It was impossible to perform astretching beyond the attainable stretching ratios, because laminatesthemselves in the reference samples 1 to 3 were finally broken. However,a possibility cannot be denied that the attainable stretching ratio ofthe PVA type resin layer itself formed on the crystallizable PET has animpact on the above result.

Referring to FIG. 18, the dotted line therein indicates an attainablestretching ratio of PVA belonging to a PVA type resin. A glasstransition temperature Tg of the PVA type resin is in the range of 75 to80° C., and a single-layer made of the PVA type resin cannot bestretched at a temperature below the glass transition temperature Tg. Asis clear from FIG. 18, the attainable stretching ratio of thesingle-layer of the PVA type resin during the elevated temperaturein-air end-free uniaxial stretching is limited to up to 5.0. Thus, theinventors have been able to clarify that, from the relationship betweenthe stretching temperature and the attainable stretching ratio of eachof a crystallizable PET and a PVA type resin, an attainable stretchingratio of a laminate comprising a crystallizable PET substrate and a PVAtype resin layer formed on the substrate, during the elevatedtemperature in-air end-free uniaxial stretching, is limited to the rangeof 4.0 to 5.0 at a stretching temperature ranging from 90 to 110° C.

An example in which a laminate prepared by coating a PVA type resinlayer on a non-crystallizable PET substrate is subjected to an end-freeuniaxial stretching in air under elevated temperature is shown ascomparative examples 1 and 2 in the following Table 1. In thenon-crystallizable PET substrate, there is no constraint of stretchingtemperature. In the comparative example 1, a polarizing film wasproduced by forming a 7 μm-thick PVA type resin layer on a 200 μm-thicknon-crystallizable PET substrate to form a laminate, and subjecting thelaminate to the elevated temperature in-air end-free uniaxial stretchingat a stretching temperature of 130° C. The stretching ratio in thecomparative example 1 was 4.0.

Referring to Table 1, in the comparative example 2, as with thecomparative example 1, polarizing films were prepared by forming a 7μm-thick PVA type resin layer on a 200 μm-thick non-crystallizable PETsubstrate to form laminates, and stretching the laminates to thestretching ratio of 4.5, 5.0 and 6.0, respectively. As illustrated inTable 1, there have been observed non-uniform stretching or breaking inthe film surfaces of the non-crystalline PET substrates, and breaking ofthe PVA type resin layer at a stretching ratio of 4.5. Based on thedata, it has been verified that the stretching ratio of the PVA typeresin layer during the elevated temperature in-air end-free uniaxialstretching at a stretching temperature of 130° C. is limited to 4.0.

TABLE 1 (COMPARATIVE TABLE) Stretched film Stretching StretchingNon-crystallizable PET substrate Laminate of PVA type resin layer andTemperature Ratio (isophthalic acid-copolymerized PET)non-crystallizable PET substrate Comparative 4.0 ∘ ∘ example 1 Uniformlystretched without Uniformly stretched without breakage breakageComparative 4.5 Δ x example 2 No breakage but occurrence of Breakage oflaminate of PVA type non-uniform stretching resin layer andnon-crystallizable PET substrate 5.0 Δ Untested No breakage butoccurrence of non-uniform stretching 6.0 x Untested Breakage

In each of the reference samples 1 to 3, although there is a differencein stretching temperature, a dyed laminate was produced by steps offorming a PVA type resin layer on a crystallizable PET substrate to forma laminate, subjecting the laminate to a stretching at a stretchingratio of 4.0 to 4.5 to allow PVA molecules to be oriented, and causingiodine to be absorbed in the thinned PVA type resin layer. Specifically,the stretched laminate was immersed in a dyeing solution containingiodine and potassium iodide under a temperature of 30° C., for anarbitrary time, to have iodine absorbed in the PVA type resin layerincluded in the stretched laminate, so that the PVA type resin layerconstituting a target polarizing film has a single layer transmittanceof 40 to 44%. In addition, the amounts of iodine to be absorbed in thethinned PVA type resin layers were adjusted to produce variouspolarizing films having different single layer transmittance T andpolarization rate P.

Referring to FIG. 26, the line 1 and the line 2 in FIG. 26 defineoptical characteristics required for a polarizing film for use in anoptical display device, according to the present invention, wherein anypolarizing film located above the line 1 or 2 in terms of therelationship between the polarization rate P and the transmittance Tsatisfies the required optical characteristics. In FIG. 26, respectiveoptical characteristics of polarizing films in the reference samples 1to 3 are illustrated in comparison with the lines 1 and 2. As seen inFIG. 26, none of the polarizing films in the reference samples 1 to 3satisfies the required optical characteristics. The reason is because itis assumed that, although PVA molecules in the PVA type resin layerformed on the crystallizable PET substrate are oriented to a certaindegree through the elevated temperature in-air stretching, the elevatedtemperature in-air stretching facilitates crystallization of the PVAmolecules preventing non-crystalline portions of the molecules frombeing oriented.

Therefore, prior to the present invention, the inventors have developeda polarizing film and a production method therefor disclosed in theinternational application PCT/JP 2010/001460. This is based on findingswith a focus on a plasticizing function of water in which a laminatecomprising a PET substrate and a PVA type resin layer formed on thesubstrate can be stretched even at a stretching temperature below aglass transition temperature Tg thereof. An example of a polarizing filmproduced by the process is shown as a comparative example 3 herein. Inaccordance with this method, the laminate comprising the PET substrateand the PVA type resin layer formed on the substrate can be stretched ata stretching ratio of up to 5.0.

Through subsequent researches, the inventors have ascertained that thestretching ratio is limited to 5.0 because the PET substrate is made ofcrystallizable PET.

Previously, the inventors have considered that the stretching functionwould not largely be affected by the crystallizing property of thesubstrate, since a laminate comprising a PET substrate and a PVA typeresin layer formed on the substrate was stretched in a boric acidaqueous solution at a temperature below a glass transition temperatureTg. However, it was found that, in cases where the PET substrate is madeof non-crystallizable PET, the laminate can be stretched at a stretchingratio of up to 5.5. It is assumed that, in a polarizing film productionmethod equivalent to the comparative example 3, the stretching ratio islimited to 5.5, due to the non-crystallizable PET substrate which posesa limit on the stretching ratio.

In the comparative example 1, various polarizing films different insingle layer transmittance T and polarization rate P were prepared.Respective optical characteristics of the polarizing films areillustrated in FIG. 26 together with those in the reference samples 1 to3.

FIG. 20 illustrates the relationship between the stretching ratiothrough the elevated temperature in-air stretching, and the overall ortotal stretching ratio (hereinafter referred to as “total stretchingratio”) under the 2-stage stretching, which has been conceived based onthe above inventors' research results, wherein the horizontal axisrepresents a stretching ratio under the elevated temperature in-airstretching at a stretching temperature of 130° C. carried out by anend-free uniaxial stretching process, and the vertical axis represents atotal stretching ratio which indicates how many times an original lengthis finally stretched by the 2-stage stretching including the elevatedtemperature in-air stretching carried out by an end-free uniaxialstretching process on an assumption that the original length, i.e., alength before the elevated temperature in-air stretching, is 1. Forexample, in the cases where the stretching ratio under the elevatedtemperature in-air stretching at a stretching temperature of 130° C. is2.0, and the stretching ratio under the second-stage stretching is 3.0,the total stretching ratio will be 6.0 (2.0×3.0=6). The second-stagestretching after the elevated temperature in-air stretching is anend-free uniaxial stretching process to be performed within a boric acidaqueous solution at a stretching temperature of 65° C. (the stretchingthrough in a boric acid aqueous solution immersion process willhereinafter be referred to as “in-boric-acid-solution stretching”). Theresult illustrated in FIG. 20 can be obtained by combining the twostretching processes.

The solid line in FIG. 20 indicates an attainable stretching ratio in anon-crystallizable PET. In the cases where the in-boric-acid-solutionstretching is directly performed without performing the elevatedtemperature in-air stretching, i.e., the stretching ratio during theelevated temperature in-air stretching is 1.0, the total stretchingratio of the non-crystallizable PET is limited to up to 5.5. Ifstretching is performed beyond this value, the non-crystallizable PETwill be broken. However, this value corresponds to the minimumstretching ratio of the non-crystallizable PET. The total stretchingratio of the non-crystallizable PET can be increased in accordance withan increase in the stretching ratio under the elevated temperaturein-air stretching, and the attainable stretching ratio can be greaterthan 10.0.

On the other hand, the dotted line in FIG. 20 indicates an attainablestretching ratio of a PVA type resin layer formed on thenon-crystallizable PET. In the cases where the in-boric-acid-solutionstretching is directly performed without performing the elevatedtemperature in-air stretching, the total stretching ratio of the PVAtype resin layer is 7.0, which is the maximum stretching ratio under theprocess. However, the total stretching ratio of the PVA type resin layerbecomes smaller along with an increase in the stretching ratio under theelevated temperature in-air stretching. At a point where the elevatedtemperature in-air stretching ratio is 3.0, the total stretching ratioof the PVA type resin layer becomes less than 6.0. If it is attempted toincrease the total stretching ratio of the PVA type resin layer up to6.0, the PVA type resin layer will be broken. As is also clear from FIG.20, depending on the level of the stretching ratio during the elevatedtemperature in-air stretching, a factor causing a laminate comprising anon-crystallizable PET substrate and a PVA type resin layer formed onthe substrate to become unable to be stretched is changed from thenon-crystallizable PET substrate to the PVA type resin layer. Forreference, the stretching ratio of PVA under the elevated temperaturein-air stretching is up to 4.0, and the PVA cannot be stretched beyondthis value. It is assumed that this stretching ratio corresponds to thetotal stretching ratio of the PVA.

Referring now to FIG. 21, there is shown a graph indicating therelationship between the stretching temperature during the elevatedtemperature in-air stretching and the total attainable stretching ratioin the 2-stage stretching consisting of the elevated temperature in-airstretching and the in-boric-acid-solution stretching, in each ofcrystallizable PET, non-crystallizable PET and PVA type resin, whereinthe graph is plotted based on experimental data. FIG. 18 illustratescharacteristics of a crystallizable PET, a non-crystallizable PET and aPVA type resin, wherein the horizontal axis represents the stretchingtemperature under the elevated temperature in-air stretching, and thevertical axis represents an attainable stretching ratio under theelevated temperature in-air stretching. FIG. 21 is different from FIG.18 in that the horizontal axis represents the stretching temperaturewhen the stretching ratio under the elevated temperature in-airstretching ratio is 2.0, and the vertical axis represents the totalattainable stretching ratio under the elevated temperature in-airstretching and the in-boric-acid-solution stretching.

The method of producing a polarizing film which can be used in thepresent invention comprises a combination of 2-stage stretching stepsconsisting of an elevated temperature in-air stretching and anin-boric-acid-solution stretching, as will be described later. Thecombination of 2-stage stretching steps is not the one which is simplyconceivable. Through various long-term researches, the inventors havefinally reached a surprising conclusion that the following two technicalproblems can be simultaneously solved only by the combination. In anattempt to produce a polarizing film by forming a PVA type resin layeron a thermoplastic resin substrate to form a laminate, and subjectingthe laminate to a stretching and dyeing, there are two technicalproblems which have been considered to be impossible to overcome.

The first technical problem is that the stretching ratio and thestretching temperature each having an impact on improvement in molecularorientation of a PVA type resin are largely restricted by thethermoplastic resin substrate on which the PVA type resin layer isformed.

The second technical problem is that, for example, even if the problemon restrictions to the stretching ratio and the stretching temperaturecan be overcome, stretching of the

PVA type resin is restricted due to its crystallization becausecrystallization and stretchability of a crystallizable resin such as thePVA type resin and PET used for the thermoplastic resin substrate areincompatible physical properties.

The first technical problem will further be discussed in the followings.One of the restrictions in producing a polarizing film using athermoplastic resin substrate is caused by the property of the PVA typeresin in that the stretching temperature is above the glass transitiontemperature Tg (about 75 to 80° C.) thereof and its attainablestretching ratio is in the range of 4.5 to 5.0. If a crystallizable PETis used as a material for the thermoplastic resin substrate, thestretching temperature is further restricted to 90 to 110° C. It hasbeen considered that any polarizing film cannot be free from the aboverestriction as long as it is produced by a process of forming a PVA typeresin layer on a thermoplastic resin substrate to form a laminate, andsubjecting the laminate to the elevated temperature in-air stretching tohave the PVA type resin layer included in the laminate decreased inthickness.

Therefore, with a focus on a plasticizing function of water, theinventors have proposed an in-boric-acid-solution stretching capable ofserving as an alternative to the elevated temperature in-air stretching.However, even in the in-boric-acid-solution stretching at a stretchingtemperature of 60 to 85° C., it has been difficult to overcome therestriction caused by the thermoplastic resin substrate, specifically, arestriction that the stretching ratio attainable in a crystallizable PETis limited to up to 5.0, and the stretching ratio in anon-crystallizable PET is limited to 5.5. These facts cause arestriction on improvement in orientation of PVA molecules, which leadsto a restriction to optical characteristics of the polarizing film of adecreased thickness. This is the first technical problem.

A solution to the first technical problem can be explained based on FIG.22. FIG. 22 includes two related graphs, one being a diagramillustrating a molecular orientation of a PET used as the thermoplasticresin substrate, and the other being a diagram illustrating the degreeof crystallization of the PET, wherein the horizontal axis commonlyrepresents the total stretching ratio obtained through the elevatedtemperature in-air stretching and the in-boric-acid-solution stretching.Each of the dotted lines in FIG. 22 indicates the total stretching ratioobtained through only the in-boric-acid-solution stretching. Regardlessof whether crystallizable or non-crystallizable, the extent ofcrystallization of the PET is sharply increased at a total stretchingratio of 4.0 to 5.0. Thus, even in cases where thein-boric-acid-solution stretching is employed, the stretching ratio islimited to 5.0 or 5.5. At this stretching ratio, the molecularorientation is maximized, and there will be a sharp increase in thestretching tension. As the result, stretching becomes no longerpossible.

On the other hand, the solid lines in FIG. 22 illustrate the result of2-stage stretching in which the elevated temperature in-air end-freeuniaxial stretching is performed at a stretching temperature of 110° C.to attain a stretching ratio of 2.0, and then the in-boric-acid-solutionstretching is performed at a stretching temperature of 65° C. Regardlessof whether crystallizable or non-crystallizable, the extent ofcrystallization of the PET is never sharply increased, differently fromthe cases where only the in-boric-acid-solution stretching is performed.This allows the total stretchable ratio to be increased up to 7.0. Atthis total stretchable ratio, the molecular orientation is maximized,and the stretching tension is sharply increased. As is clear from FIG.21, this would result from employing the elevated temperature in-airend-free uniaxial stretching as the first-stage stretching. In contrast,if the elevated temperature in-air stretching is performed whileconstraining contraction in a direction perpendicular to the directionof the stretching, i.e., based on a so-called “end-fixed uniaxialstretching process”, as described later, the total attainable stretchingratio can be increased up to 8.5.

The relationship between the molecular orientation and the extent ofcrystallization of the PET used as a material for the thermoplasticresin substrate, illustrated in FIG. 22, shows that crystallization ofthe PET can be suppressed, regardless of whether crystallizable ornon-crystallizable, by performing a preliminary stretching based on theelevated temperature in-air stretching. However, referring to FIG. 23which illustrates the relationship between the preliminary stretchingtemperature and the molecular orientation of the PET, it is noted that,in cases where a crystallizable PET is used as a material for thethermoplastic resin substrate, the molecular orientation of thecrystallizable PET after the preliminary stretching is 0.30 or more at90° C., 0.20 or more at 100° C., and 0.10 or more even at 110° C. If themolecular orientation of the PET becomes equal to or greater than 0.10,there will be an increase in the stretching tension in the second-stagestretching performed within a boric acid aqueous solution, and therewill be a corresponding increase in the load imposed on the stretchingapparatus, which is undesirable in terms of production conditions. FIG.23 shows that it is preferable to use, as a material for thethermoplastic resin substrate, a non-crystallizable PET, more preferablya non-crystallizable PET having an orientation function of 0.10 or less,particularly preferably a non-crystallizable PET having an orientationfunction of 0.05 or less.

FIG. 23 illustrates experimental data indicating the relationshipbetween the stretching temperature in the elevated temperature in-airstretching at a stretching ratio of 1.8 and the orientation function ofthe PET used as a material for the thermoplastic resin substrate. As isclear from FIG. 23, in the case where a non-crystallizable PET is used,it is possible to make the PET to have an orientation function of 0.10or less allowing a stretched laminate to be stretched within a boricacid aqueous solution to a high stretching ratio. Particularly, in thecases where the orientation function is 0.05 or less, thenon-crystallizable PET can be steadily stretched at a high stretchingratio without subjecting the stretching apparatus to a substantial loadwhich may cause, for example, increase in the stretching tension, duringthe second-stage in-boric-acid-solution stretching. This feature canalso be easily understood from values of the orientation function in theExamples 1 to 18 and the reference samples 1 to 3 in FIG. 29.

By solving the first technical problem, it has become possible toeliminate restrictions to the stretching ratio which would otherwise becaused by the PET substrate, and increase the total stretching ratio toimprove the molecular orientation of the PVA type resin. Thus, opticalcharacteristics of the polarizing film can be significantly improved.However, an improvement in the optical characteristics achieved by theinventors is not limited thereto. Further improvement will be achievedby solving the second technical problem.

The second technical problem will further be discussed in thefollowings. One of the features inherent to a PVA type resin and acrystallizable resin such as PET as a material for the thermoplasticresin substrate is that, in general, polymer molecules are orderlyarranged by heating and stretching/orienting and thereby crystallizationis progressed. Stretching of the PVA type resin is restricted bycrystallization of the PVA type resin which is a crystallizable resin.Crystallization and stretchability are mutually incompatible physicalproperties, and it has been commonly recognized that progress incrystallization of the PVA type resin hinders the molecular orientationof the PVA type resin. This is the second technical problem. Means forsolving the second technical problem can be explained based on FIG. 24.In FIG. 24, each of the solid line and the dotted line indicates therelationship between the extent of crystallization and the orientationfunction of the PVA type resin, calculated based on two experimentalresults.

The solid line in FIG. 24 indicates the relationship between the extentof crystallization and the orientation function of a PVA type resin ineach of six samples provided in the following manner. Firstly, sixlaminates each comprising a non-crystallizable PET substrate and a PVAtype resin layer formed on the substrate were prepared under the sameconditions. The prepared six laminates each including the PVA type resinlayer were subjected to the elevated temperature in-air stretching,respectively, at different stretching temperatures of 80° C., 95° C.,110° C., 130° C., 150° C. and 170° C., to attain the same stretchingratio of 1.8, so as to obtain six stretched laminates each including aPVA type resin layer. Then, the extent of crystallization of the PVAtype resin layer included in each of the stretched laminates and theorientation function of the PVA type resin were measured and analyzed.Details of methods of the measurement and analysis will be describedlater.

Similarly, the dotted line in FIG. 24 indicates the relationship betweenthe extent of crystallization and the orientation function of a PVA typeresin layer in each of six samples provided in the following manner.Firstly, six laminates each comprising a non-crystallizable PETsubstrate and a PVA type resin layer formed on the substrate wereprepared under the same conditions. The prepared six laminates eachincluding the PVA type resin layer were stretched by the elevatedtemperature in-air stretching at the same stretching temperature of 130°C. to attain different stretching ratios of 1.2, 1.5, 1.8, 2.2, 2.5 and3.0, respectively, so as to obtain six stretched laminates eachincluding a PVA type resin layer. Then, the extent of crystallization ofthe PVA type resin layer included in each of the stretched laminates andan orientation function of the PVA type resin were measured and analyzedby the methods described later.

The solid line in FIG. 24 shows that the molecular orientation of thePVA type resin included in the stretched laminate is improved as thestretching temperature during the elevated temperature in-air stretchingis set to a higher value. Further, the dotted line in FIG. 24 shows thatthe molecular orientation of the PVA type resin included in thestretched laminate is improved as the stretching ratio during theelevated temperature in-air stretching is set to a higher value. Inother words, in advance of the second-stage in-boric-acid-solutionstretching, the molecular orientation of the PVA type resin is improved,i.e., the extent of crystallization of the PVA type resin is increased.This leads to improvement in molecular orientation of the PVA type resinafter the in-boric-acid-solution stretching. In addition, theimprovement in molecular orientation of the PVA type resin leads to animprovement in orientation of polyiodide ions. This can be ascertainedfrom the T-P graphs of the Examples as described later.

As above, it has been possible to attain an unanticipated remarkableresult in that the orientation of PVA molecules in the PVA type resinlayer formed by the second-stage in-boric-acid-solution stretching canbe further improved by setting the stretching temperature or thestretching ratio during the first-stage elevated temperature in-airstretching to a higher value.

Reference will now be made to the crystallization degree or extent ofcrystallization (horizontal axis) of the PVA type resin illustrated inFIG. 24. Preferably, the extent of crystallization or thecrystallization degree of PVA type resin layer should be 27% or more soas to allow a dyed laminate to be formed without causing a problem suchas dissolution of the PVA type resin layer, in a dyeing step ofimmersing the stretched laminate including the PVA type resin layer in adyeing aqueous solution. This makes it possible to dye the PVA typeresin layer without causing dissolution of the PVA type resin layer. Thecrystallization degree of the PVA type resin layer may be set to 30% ormore. In this case, the stretching temperature during thein-boric-acid-solution stretching can be increased. This makes itpossible to stably perform the stretching of the dyed laminate andstably produce a polarizing film.

On the other hand, if the crystallization degree of the PVA type resinlayer is 37% or more, dyeability of the PVA type resin layer will bedeteriorated, and thereby it is necessary to increase a concentration ofthe dyeing aqueous solution, so that an amount of material to be used,and a required time for the dyeing, will be increased, which is likelyto cause deterioration in productivity. If the crystallization degree ofthe PVA type resin layer is set to 40% or more, another problem, such asbreaking of the PVA type resin layer during the in-boric-acid-solutionstretching, is likely to occur. Therefore, the extent of crystallizationor the crystallization degree of the PVA type resin is preferablydetermined in the range of 27% to 40%, more preferably in the range of30% to 37%.

Reference is now made to the orientation function (vertical axis) of thePVA type resin layer illustrated in FIG. 24. Preferably, the orientationfunction of the PVA resin layer is set to 0.05 or more so as to allow ahighly functional polarizing film to be prepared using anon-crystallizable PET resin substrate. The orientation function of thePVA type resin layer may be set to 0.15 or more. In this case, thestretching ratio during the in-boric-acid-solution stretching for thedyed laminate including the PVA type resin layer can be reduced. Thismakes it possible to prepare a polarizing film having a larger width.

On the other hand, if the orientation function of the PVA type resinlayer is set to 0.30 or more, the dyeability will be deteriorated, andthereby it is necessary to increase the concentration of the dyeingaqueous solution, so that an amount of material to be used, and arequired time for the dyeing, will be increased, which is likely tocause deterioration in productivity. If the orientation function of thePVA type resin layer is set to 0.35 or more, another problem, such asbreaking of the PVA type resin layer during the in-boric-acid-solutionstretching, is likely to occur. Therefore, the orientation function ofthe PVA type resin is preferably set in the range of 0.05 to 0.35, morepreferably in the range of 0.15 to 0.30.

Means for solving the first technical problem is to auxiliarily orpreliminarily stretch a laminate comprising a non-crystallizable PETsubstrate and a PVA type resin layer formed on the substrate by thefirst-stage elevated temperature in-air stretching, whereby the PVA typeresin layer can be stretched at a higher stretching ratio by thesecond-stage in-boric-acid-solution stretching without being restrictedby the stretching ratio of the non-crystallizable PET substrate, so thatthe molecular orientation of the PVA is sufficiently improved.

Means for solving the second technical problem is to auxiliarily orpreliminarily set the stretching temperature during the first-stageelevated temperature in-air stretching to a higher value, or auxiliarilyor preliminarily set the stretching ratio during the first-stageelevated temperature in-air stretching to a higher value, whereby anunanticipated result has been provided that the orientation of PVAmolecules in the PVA type resin layer formed by the second-stagein-boric-acid-solution stretching is further improved. In either case,the first-stage elevated temperature in-air stretching can be regardedas auxiliary or preliminary in-air stretching means for the second-stagein-boric-acid-solution stretching. The “first-stage elevated temperaturein-air stretching” will hereinafter be referred to as “preliminaryin-air stretching”, in contrast to the second-stagein-boric-acid-solution stretching.

In particular, a mechanism for solving the second technical problem byperforming the “preliminary in-air stretching” can be assumed asfollows. As is ascertained in FIG. 24, the molecular orientation of thePVA type resin after the preliminary in-air stretching is improved asthe preliminary in-air stretching is performed at a higher temperatureor a higher ratio. It is assumed that this is because the stretching isperformed in a more progressed state of crystallization of the PVA typeresin as the stretching temperature or rate becomes higher.Consequently, the molecular orientation of the PVA type resin isimproved. In this manner, the molecular orientation of the PVA typeresin is improved by the preliminary in-air stretching in advance of thein-boric-acid-solution stretching. In this case, it is assumed that,when the PVA type resin is immersed in a boric acid aqueous solution,boric acid can be easily cross-linked with the PVA type resin, and thestretching is performed under a condition that nodes are being formed bythe boric acid. Consequently, the molecular orientation of the PVA typeresin is further improved after the in-boric-acid-solution stretching.

Considering all the above factors together, a polarizing film having athickness of 10 μm or less and optical characteristics satisfying thefollowing condition (1) or (2) can be obtained by performing astretching based on a 2-stage stretching consisting of a preliminaryin-air stretching and an in-boric-acid-solution stretching:

P>−(10^(0.929T−42.4)−1)×100 (where T<42.3); and

P≧99.9 (where T≧42.3), or   Condition (1)

T≧42.5; and

P>99.5   Condition (2)

wherein T is a single layer transmittance, and P is a polarization rate.The dichroic material may be iodine or a mixture of iodine and anorganic dye.

A polarizing film having optical characteristics in which the singlelayer transmittance T and the polarization rate P fall within the rangesrepresented by the above conditions fundamentally has a performancerequired for use in a display device for a liquid-crystal televisionusing a large-sized display element, or performance required for use inan organic EL display device. More specifically, for liquid-crystaltelevisions, it is possible to produce an optical display device havinga contrast ratio of 1000:1 or more, and, a maximum luminance of 500cd/m² or more. In this specification, this performance will be referredto as “required performance”. This polarizing film can also be used inan optically functional film laminate to be laminated to a viewing sideof an organic EL display panel.

When used with a liquid-crystal display panel, a polarizing film to bedisposed on one of a backlight and viewing sides of the liquid-crystaldisplay panel must have polarization performance satisfying at least theabove optical characteristics. Further, in cases where a polarizing filmhaving a polarization rate of 99.9% or less is disposed on one of thebacklight and viewing sides, it will become difficult to achieve therequired performance, even if a polarizing film having highest possiblepolarization performance is disposed on the other side.

Reference will now be made to FIG. 1. FIG. 1 illustrates the result ofverification on whether the thickness of a non-crystallizable ester typethermoplastic resin substrate and the coating thickness of a PVA typeresin layer (a thickness of a polarizing film) are likely to pose acertain problem. In FIG. 1, the horizontal axis represents the thicknessof the thermoplastic resin substrate designated in units of μm, and thevertical axis represents the thickness of the PVA type resin layercoated on the substrate. On the vertical axis, the numeral inparentheses indicates the thickness of a polarizing film formed bysubjecting the PVA type resin layer on the substrate to a stretching anddyeing. As illustrated in FIG. 1, if the thickness of the substrate is 5times or less the thickness of PVA type resin layer, a problem is likelyto occur in terms of transportability or feedability. On the other hand,if the thickness of the polarizing film obtained through the stretchingand dyeing becomes equal to or greater than 10 μm, a problem is likelyto occur in terms of crack resistance of the polarizing film.

As a material for the thermoplastic resin substrate, it is preferable touse a non-crystallizable ester type resin. This type of thermoplasticresin may be a non-crystallizable polyethylene terephthalate comprisingcopolymerized polyethylene terephthalate which includes isophthalicacid-copolymerized polyethylene terephthalate andcyclohexanedimethanol-copolymerized polyethylene terephthalate. Thesubstrate may be made of a transparent resin. Although the abovedescription has been made based on an example in which anon-crystallizable resin material is used as the thermoplastic resinsubstrate, a crystallizable resin material may also be used.

Preferably, a dichroic material for dyeing a polyvinyl alcohol typeresin is iodine, or a mixture of iodine and an organic dye.

In the present invention, an optically functional film may be bonded toa polarizing film made of the PVA type resin layer on the thermoplasticresin substrate. Further, after peeling the resin substrate from thepolarizing film, a separator film may be releasably laminated to asurface of the polarizing film from which the resin substrate is peeled,through an adhesive layer. The separator film is treated to have theadhesion force thereof to the adhesive layer weaker than an adhesionforce of the polarizing film to the adhesive layer, so that, when theseparator film is peeled from the polarizing film, the adhesive layer isleft on the side of the polarizing film. In cases where a roll of anoptical film laminate to be produced according to the present inventionis used for manufacturing display devices, the separator film may beused as a carrier film. Alternatively, the separator may be used only asa medium for giving an adhesive layer to the polarizing film.

In another embodiment of the present invention, an optically functionalfilm laminate may be formed by attaching an optically functional film toa surface of the thermoplastic resin substrate, such as anon-crystallizable ester type thermoplastic resin substrate, on whichthe polarizing film is not formed, and releasably laminating a separatorfilm onto the optically functional film through an adhesive layer. Inthis case, the optically functional film may be one of a plurality ofconventional optically functional films incorporated in display devicesso as to achieve various optical functions. The optically functionalfilm may include the aforementioned ¼ wavelength phase difference film.There have also been known various optically functional film used forviewing angle compensation. In another embodiment, after attaching anoptically functional film to a surface of the polarizing film on a sideopposite to the thermoplastic resin substrate, a film, such as aprotective film, may be attached onto the optically functional filmthrough an adhesive layer. Then, after peeling the thermoplastic resinsubstrate, a separator film may be bonded to a surface of the polarizingfilm from which the substrate is peeled, through an adhesive layer. Adefect inspection may be performed after peeling the separator film.Then, after completion of the inspection, the peeled separator film or anewly prepared separator film may be bonded to the polarizing filmthrough an adhesive layer.

As is evidenced from FIG. 1, the thickness of the thermoplastic resinsubstrate, such as the non-crystallizable ester type thermoplastic resinsubstrate is preferably 6 times or more, more preferably 7 times ormore, the thickness of the PVA type resin layer formed on the substrate.In cases where the thickness of the non-crystallizable ester typethermoplastic resin substrate is 6 times or more with respect to the PVAtype resin layer, it becomes possible to prevent the occurrence ofproblems in terms of transportability or feedability, e.g., breakingduring transportation or feeding in a production process due toexcessively low film strength, or problems in terms of curling andtransferability of the polarizing film when it is disposed on one ofbacklight and viewing sides of a liquid-crystal display device.

Preferably, the non-crystallizable ester type thermoplastic resinsubstrate is made of a material selected from the group includingnon-crystallizable polyethylene terephthalate comprising copolymerizedpolyethylene terephthalate which includes isophthalic acid-copolymerizedpolyethylene terephthalate and cyclohexanedimethanol-copolymerizedpolyethylene terephthalate, wherein the copolymerized polyethyleneterephthalate is set to have an orientation function of 0.10 or less andsubjected to the elevated temperature in-air stretching. The substratemay be made of a transparent resin.

In implementation of the method of the present invention, wherein apolarizing film comprising a PVA type resin, using a thermoplastic resinsubstrate, an insolubilization process for insolubilizing the PVA typeresin is regarded as a key technical problem as will be specificallydescribed below.

In cases where the PVA type resin layer formed on the thermoplasticresin substrate is subjected to a stretching, it is not easy to causeiodine to be impregnated in the PVA type resin layer, while preventingthe PVA type resin layer included in a stretched intermediate product ora stretched laminate from being dissolved in a dyeing solution. In aproduction process of a polarizing film, a step of causing iodine to beabsorbed in a thinned PVA type resin layer is essential. In aconventional dyeing step, an amount of iodine to be absorbed in the PVAtype resin layer is adjusted by using a plurality of dyeing solutionshaving different iodine concentrations ranging from 0.12 to 0.25 wt %,and keeping an immersion time constant. In such a conventional dyeingstep, dissolution of the PVA type resin layer will occur duringproduction of a polarizing film to preclude dyeing. As used here, theterm “concentration” means a mixing ratio with respect to a total amountof the solution. Further, the term “iodine concentration” means a mixingratio of iodine to a total amount of the solution, wherein an amount ofiodine added as an iodide such as potassium iodide is not includedtherein. In the following description, the terms “concentration” and“iodine concentration” will be used as the same meanings.

As is clear from the test result illustrated in FIG. 6, the abovetechnical problem can be solved by setting a concentration of iodine asthe dichroic material to 0.3 wt % or more. Specifically, a plurality ofpolarizing films having various polarization performances can beproduced by subjecting the stretched laminate including a stretchedintermediate product comprising a PVA type resin layer to dyeing processusing dyeing solutions different in iodine concentration, whileadjusting an immersion time for the dyeing to form various dyedlaminates each including a dyed intermediate product, and thensubjecting the dyed laminates to the in-boric-acid-solution stretching.

Reference will now be made to FIG. 7, there is shown that there is nosignificant difference in polarization performance between thepolarizing films formed by adjusting the iodine concentration to 0.2 wt%, 0.5 wt % and 1.0 wt %, respectively. Meanwhile, in order to realizedyeing excellent in uniformity during formation of a dyed laminateincluding a dyed intermediate product, it is preferable to reduce theiodine concentration so as to ensure a stable immersion time, ratherthan increasing the iodine concentration so as to perform the dyeingwithin a shorter immersion time.

Referring to FIG. 8, there is shown that two different insolubilizationsduring implementation of the present invention (hereinafter referred toas “first and second insolubilizations”) also have influences on theoptical characteristics of the target polarizing film. FIG. 8 can beconsidered as a result of analysis on functions of the first and secondinsolubilizations for the thinned PVA type resin layer. FIG. 8illustrates respective optical characteristics of polarizing filmsproduced based on the four Examples 1 to 4, each satisfying the requiredperformance for a display device of a liquid-crystal television using alarge-sized display element.

The Example 1 indicates optical characteristics of polarizing filmsproduced without conducting the first and the second insolubilizationsteps. The Example 2 indicates optical characteristics of polarizingfilms produced by performing only the second insolubilization stepwithout performing the first insolubilization step, and the Example 3indicates optical characteristics of polarizing films produced byperformed only the first insolubilization step without performing thesecond insolubilization step. The Example 4 indicates opticalcharacteristics of polarizing films produced by performing both thefirst and second insolubilization steps.

In the present invention, a polarizing film satisfying the requiredperformance can be produced without conducting the aftermentioned firstand the second insolubilization steps which will be described later.However, as is clear from FIG. 8, the optical characteristics of thenon-insolubilized polarizing films in the Example 1 are inferior tothose of the polarizing films in the Examples 2 to 4. Comparingrespective optical characteristics of the Examples 1 to 4, the level ofthe optical characteristics becomes higher in the following order:Example 1<Example 3<Example 2<Example 4. In each of the Examples 1 and2, a dyeing solution having an iodine concentration of 0.3 wt % and apotassium iodide concentration of 2.1 wt % was used. Differently, in theExamples 3 and 4, a plurality of types of dyeing solutions having aniodine concentration ranging from 0.12 to 0.25 wt % and a potassiumiodide concentration ranging from 0.84 to 1.75 wt % were used. Asignificant difference between the group of the Examples 1 and 3 and thegroup of the Examples 2 and 4 is that the dyed intermediate product inthe former group is not subjected to the insolubilization, whereas thedyed intermediate product in the latter group is subjected to theinsolubilization. In the Example 4, not only the dyed intermediateproduct but also the stretched intermediate product before the dyeingare subjected to the insolubilization. Through the first and secondinsolubilizations, optical characteristics of the polarizing film couldbe significantly improved.

As is clear from FIG. 7, the mechanism for improving opticalcharacteristics of a polarizing film is not based on the iodineconcentration of the dyeing solution, but based on functions of thefirst and second insolubilizations. This finding can be regarded asmeans for solving a third technical problem in the production method ofthe present invention.

In one embodiment of the present invention, the first insolubilizationis designed to prevent dissolution of the thinned PVA type resin layerincluded in the stretched intermediate product (or stretched laminate).On the other hand, the second insolubilization included in thecross-linking step is designed to stabilize dyeing so as to preventiodine absorbed in the PVA type resin layer included in the dyedintermediate product (or a dyed laminate) from being eluted during thein-boric-acid-solution stretching at a solution temperature of 75° C. ina subsequent step, and prevent dissolution of the thinned PVA type resinlayer.

If the second insolubilization is omitted, elution of the iodineimpregnated in the PVA type resin layer will be progressed during thein-boric-acid-solution stretching at a solution temperature of 75° C.,so that the PVA resin layer will be acceleratedly dissolved. The elutionof iodine and dissolution of the PVA type resin layer can be avoided bylowering a temperature of the boric acid aqueous solution. For example,it is necessary to stretch a dyed intermediate product (or dyedlaminate) while immersing it in the boric acid aqueous solution at asolution temperature of less than 65° C. However, this reduces theeffect of the plasticizing function of water, so that softening of thePVA type resin layer included in the dyed intermediate product (or dyedlaminate) is not sufficiently obtained. This results in deterioration inthe stretching performance, so that the dyed intermediate product (ordyed laminate) is likely to break during the course of thein-boric-acid-solution stretching. It should be understood that anintended total stretching ratio of the PVA type resin layer cannot beattained.

[Outline of Production Process]

With reference to the drawings, one example of a process of producing apolarizing film for use in the present invention will be describedbelow.

Referring to FIG. 9, there is shown a schematic diagram illustrating aproduction process for an optical film laminate 10 comprising apolarizing film 3, without an insolubilization step. In the following,descriptions will be made on a process of producing an optical filmlaminate 10 comprising a polarizing film 3 in accordance with theExample 1.

As a thermoplastic resin substrate, there has been prepared a continuousweb of a substrate made of isophthalic acid-copolymerized polyethyleneterephthalate copolymerized with isophthalic acid in an amount of 6 mol% (hereinafter referred to as “non-crystallizable PET”). A laminate 7comprising a continuous web of a non-crystallizable PET substrate 1having a glass transition temperature Tg of 75° C., and a PVA layer 2having a glass transition temperature Tg of 80° C. was prepared in thefollowing manner.

(Laminate Preparation Step (A))

Firstly, a non-crystallizable PET substrate 1 having a thickness of 200μm, and a PVA solution prepared by dissolving a PVA powder having apolymerization degree of 1000 or more and a saponification degree of 99%or more, in water to have a concentration of 4 to 5 wt % were prepared.Then, in a laminate forming apparatus 20 equipped with a coating unit21, a drying unit 22 and a surface modifying unit 23, the PVA solutionwas applied to the non-crystallizable PET substrate 1 having a thicknessof 200 μm, and dried at a temperature of 50 to 60° C., to form a 7μm-thick PVA layer 2 on the non-crystallizable PET substrate 1. Thethickness of the PVA layer can be appropriately changed, as describedlater. The laminate obtained in the above manner will hereinafter bereferred to as a “laminate 7 comprising a non-crystallizable PETsubstrate and a PVA layer formed on the substrate”, or as a “PVAlayer-including laminate 7”, or simply as a “laminate 7”.

A laminate 7 including a PVA layer will be produced in the form of apolarizing film 3 having a thickness of 3 μm through the followingprocesses including a 2-stage stretching step consisting of apreliminary in-air stretching and an in-boric-acid-solution stretching.While the present invention is intended to use a polarizing film havinga thickness of 10 μm or less, any polarizing film having an arbitrarythickness of 10 μm or less can be formed by appropriately changing thethickness of a PVA type resin layer to be formed on the PET substrate 1.

(Preliminary In-Air Stretching Step (B))

In a first-stage preliminary in-air stretching step (B), the laminate 7including the 7 μm-thick PVA layer 2 was stretched together with thenon-crystallizable PET substrate 1 to form a “stretched laminate 8”including a 5 μm-thick PVA layer 2. Specifically, in a preliminaryin-air stretching apparatus 30 having stretching means 31 providedwithin an oven 33, the laminate 7 including the 7 μm-thick PVA layer 2was fed to pass through the stretching means 31 within the oven 33 setto a temperature environment of 130° C., so that it was subjected to anend-free uniaxial stretching to attain a stretching ratio of 1.8 tothereby form a stretched laminate 8. At this stage, the stretchedlaminate 8 may be wound on a take-up unit 32 provided in side-by-siderelation to the oven 33, to produce a roll 8′ of the stretched laminate8.

Now, “end-free stretching” and “end-fixed stretching” will be generallydescribed. When a film of a substantial length is stretched in atransportation or feeding direction, the film is reduced in size in adirection perpendicular to the direction of the stretching, i.e. in awidthwise direction of the film. The end-free stretching means atechnique of performing a stretching without suppressing such reductionin width. “Longitudinal uniaxial stretching” is a technique ofperforming a stretching only in a longitudinal direction of the film.The end-free uniaxial stretching is generally used in contrast with theend-fixed uniaxial stretching which is a technique of performing astretching while suppressing the shrinkage or contraction which wouldotherwise occur in a direction perpendicular to the stretchingdirection. Through the end-free uniaxial stretching, the 7 μm-thick PVAlayer 2 included in the laminate 7 is converted into a 5 μm-thick PVAlayer 2 in which PVA molecules are oriented in the stretching direction.

(Dyeing Step (C))

Then, in a dyeing step (C), a dyed laminate 9 was formed in which iodineas a dichroic material is absorbed in the 5 μm-thick PVA layer 2 havingthe oriented PVA molecules. Specifically, in a dyeing apparatus 40equipped with a dyeing bath 42 of a dyeing solution 41 containing iodineand potassium iodide, the stretched laminate 8 unrolled from a feedingunit 43 provided in side-by-side relation to the dyeing apparatus 40 andloaded with the roll 8′ was immersed in the dyeing solution 41 at asolution temperature of 30° C., for an appropriate time, to allow a PVAlayer making up a target polarizing film 3 (to be finally formed) tohave a single layer transmittance of 40 to 44%. In this manner, a dyedlaminate 9 was formed in which iodine is absorbed in the molecularlyoriented PVA layer 2 of the stretched laminate 8.

In the above step, in order to prevent dissolution of the PVA layer 2included in the stretched laminate 8, the dyeing solution 41 was formedas an aqueous solvent having an iodine concentration of 0.30 wt %.Further, the dyeing solution 41 was adjusted to allow a concentration ofpotassium iodide for allowing iodine to be dissolved in water to become2.1 wt %. The ratio of the iodine concentration to the potassium iodideconcentration was 1:7. More specifically, the laminate 8 was immersed inthe dyeing solution 41 having an iodine concentration of 0.30 wt % and apotassium iodide concentration of 2.1 wt %, for 60 seconds, to form adyed laminate 9 having iodine absorbed in the 5 μm-thick PVA layer 2having the oriented PVA molecules. In the Example 1, the immersion timeof the stretched laminate 8 in the dyeing solution 41 having an iodineconcentration of 0.30 wt % and a potassium iodide concentration of 2.1wt % was changed to adjust an amount of iodine to be absorbed, so as toallow a target polarizing film 3 to have a single layer transmittance of40 to 44%, to form various dyed laminates 9 different in single layertransmittance and polarization rate.

(In-Boric-Acid-Solution Stretching Step (D))

In a second-stage in-boric-acid-solution stretching step (D), the dyedlaminate 9 including the PVA layer 2 which was already dyed withmolecularly oriented iodine was further stretched to form an opticalfilm laminate 10 which includes the PVA layer having molecularlyoriented iodine and making up a 3 μm-thick polarizing film 3.Specifically, in an in-boric-acid-solution stretching apparatus 50equipped with stretching means 53 and a bath 52 of a boric acid aqueoussolution 51 containing boric acid and potassium iodide, the dyedlaminate 9 continuously fed from the dyeing apparatus 40 was immersed inthe boric acid aqueous solution 51 set to a solution temperatureenvironment of 65° C., and then fed to pass through the stretching means53 provided in the in-boric-acid-solution stretching apparatus 50, sothat it was subjected to an end-free uniaxial stretching to attain astretching ratio of 3.3 to thereby form the optical film laminate 10.

More specifically, the boric acid aqueous solution 51 was adjusted tocontain 4 weight parts of boric acid with respect to 100 weight parts ofwater, and 5 weight parts of potassium iodide with respect to 100 weightparts of water. In this step, the dyed laminate 9 having the absorbediodine in an adjusted amount was first immersed in the boric acidaqueous solution 51 for 5 to 10 seconds. Then, the dyed laminate 9 wasfed to directly pass through between a plurality of sets of rollsdifferent in circumferential speed, as the stretching means 53 of thein-boric-acid-solution stretching apparatus 50, so that it was subjectedto an end-free uniaxial stretching to attain a stretching ratio of 3.3while taking a time of 30 to 90 seconds. Through this stretching, thePVA layer included in the dyed laminate 9 was changed into a 3 μnm-thickPVA layer in which the absorbed iodine is highly oriented in onedirection in the form of a polyiodide ion complex. This PVA layer makesup a polarizing film 3 of the optical film laminate 10.

As described above, in the Example 1, the laminate 7 comprising anon-crystallizable PET substrate 1 and a 7 μm-thick PVA layer 2 formedon the substrate 1 is subjected to a preliminarily in-air stretching ata stretching temperature of 130° C. to form a stretched laminate 8, andthen the stretched laminate 8 is subjected to dyeing to form a dyedlaminate 9. Further, the dyed laminate 9 is subjected to anin-boric-acid-solution stretching at a stretching temperature of 65° C.to form an optical film laminate 10 including a 3 μm-thick PVA layerstretched integrally with the non-crystallizable PET substrate to attaina total stretching ratio of 5.94. Through the above 2-stage stretching,it becomes possible to form an optical film laminate 10 including a 3μm-thick PVA layer making up a polarizing film 3 in which iodineabsorbed therein through dyeing is highly oriented in the form of apolyiodide ion complex. Preferably, the optical film laminate 10 will becompleted through subsequent cleaning, drying and transfer steps.Details of the cleaning step (G), the drying step (H) and the transferstep (I) will be described in connection with a production process basedon the Example 4 incorporating an insolubilization step.

[Outline of Other Production Process]

Referring to FIG. 10, there is shown a schematic diagram illustrating aproduction process of an optical film laminate 10 including a polarizingfilm 3, which has an insolubilization step. The following descriptionwill be made about a production process of an optical film laminate 10including a polarizing film 3 based on the Example 4. As is clear fromFIG. 10, the production process based on the Example 4 may be assumed asa production process in which the first insolubilization step before thedyeing step and the cross-linking step including the secondinsolubilization before the in-boric-acid-solution stretching areincorporated into the production process based on the Example 1. Alaminate preparation step (A), a preliminary in-air stretching step (B),a dyeing step (C) and an in-boric-acid-solution stretching step (D)incorporated in this process are the same as those in the productionprocess based on the Example 1, except a difference in temperature ofthe boric acid aqueous solution for the in-boric-acid-solutionstretching step. Thus, descriptions of this process will be simplified,and the first insolubilization step before the dyeing step and thecross-linking step including the second insolubilization before thein-boric-acid-solution stretching step will be primarily described.

(First Insolubilization Step (E))

The first insolubilization step is an insolubilization step (E) prior tothe dyeing step (C). As with the production process based on the Example1, in the laminate preparation step (A), a laminate 7 comprising anon-crystallizable PET substrate and a 7 μm-thick PVA layer 2 formed onthe substrate is produced. Then, in the preliminary in-air stretchingstep (B), the laminate 7 including the 7 μm-thick PVA layer 2 issubjected to a preliminary in-air stretching to form a stretchedlaminate 8 including a 5 μm-thick PVA layer 2. Subsequently, in thefirst insolubilization step (E), the stretched laminate 8 unrolled fromthe feeding unit 43 loaded with the roll 8′ is subjected toinsolubilization to form the insolubilized stretched laminate 8″. Itshould be understood that the stretched laminate 8″ insolubilized inthis step includes an insolubilized PVA layer 2. This laminate 8″ willhereinafter be referred to as an “insolubilized stretched laminate 8″″.

Specifically, in an insolubilization apparatus 60 containing aninsolubilizing boric acid aqueous solution 61, the stretched laminate 8is immersed in the insolubilizing boric acid aqueous solution 61 at asolution temperature of 30° C., for 30 seconds. The insolubilizing boricacid solution 61 used in this step contains 3 weight parts of boric acidwith respect to 100 weight parts of water (hereinafter referred to as“insolubilizing boric acid aqueous solution”). This step is intended tosubject the stretched laminate 8 to insolubilization so as to preventthe 5 μm-thick PVA layer included in the stretched laminate 8 from beingdissolved at least during the subsequent dyeing step (C).

After the insolubilization, the insolubilized stretched laminate 8 istransported to the dyeing step (C). Differently from the Example 1, inthis dyeing step (C), a plurality of dyeing solutions are prepared bychanging the iodine concentration in the range of 0.12 to 0.25 wt %.Then, various dyed laminates 9 different in single layer transmittanceand polarization rate are formed by using the dyeing solutions whilekeeping the immersion time of the insolubilized stretched laminate 8″ ineach of the dyeing solutions constant, to adjust an amount of iodine tobe absorbed, so as to allow a target polarizing film to have a singlelayer transmittance of 40 to 44%. Even after the immersion in the dyeingsolutions having an iodine concentration of 0.12 to 0.25 wt %, the PVAlayer in the insolubilized stretched laminate 8″ is never dissolved.

(Cross-Linking Step Including Second Insolubilization (F))

The following cross-linking step may be considered as including thesecond insolubilization step, in view of the following purpose. Thecross-linking step is intended to achieve firstly insolubilization forpreventing dissolution of the PVA layer included in the dyed laminate 9during the subsequent an in-boric-acid-solution stretching step (D),secondly stabilization in dyeing for preventing elution of iodineabsorbed in the PVA layer; and thirdly formation of nodes bycross-linking of molecules in the PVA layer. The second insolubilizationis intended to accomplish the results of the aforementioned first andsecond aims.

The cross-linking step (F) is performed as a pretreatment for thein-boric-acid-solution stretching step (D). The dyed laminate 9 formedin the dyeing step (C) is subjected to cross-linking to form across-linked dyed laminate 9′. The cross-linked dyed laminate 9′includes a cross-linked PVA layer 2. Specifically, in a cross-linkingapparatus 70 containing an aqueous solution 71 comprising iodine andpotassium iodide (hereinafter referred to as “cross-linking boric acidaqueous solution”), the dyed laminate 9 is immersed in the cross-linkingboric acid solution 71 at 40° C., for 60 seconds, so as to cross-linkthe PVA molecules of the PVA layer having the absorbed iodine, to form across-linked dyed laminate 9′. The cross-linking boric acid aqueoussolution 71 used in this step contains 3 weight parts of boric acid withrespect to 100 weight parts of water, and 3 weight parts of potassiumiodide with respect to 100 weight parts of water.

In the in-boric-acid-solution stretching step (D), the cross-linked dyedlaminate 9′ is immersed in the boric acid aqueous solution at 75° C.,and subjected to an end-free uniaxial stretching to attain a stretchingratio of 3.3 to thereby form an optical film laminate 10. Through thisstretching, the PVA layer 2 included in the dyed laminate 9′ and havingabsorbed iodine is changed into a 3 μm-thick PVA layer 2 in which theabsorbed iodine is highly oriented in one direction in the form of apolyiodide ion complex. This PVA layer makes up a polarizing film 3 ofthe optical film laminate 10.

In the Example 4, a 7 μm-thick PVA layer 2 is first formed on anon-crystallizable PET substrate 1 to form a laminate 7, and then thelaminate 7 is subjected to a preliminary in-air stretching at astretching temperature of 130° C. based on an end-free uniaxialstretching process to attain a stretching ratio of 1.8 to thereby form astretched laminate 8. Then, the formed stretched laminate 8 is immersedin the insolubilizing boric acid aqueous solution 61 at a solutiontemperature of 30° C. to insolubilize the PVA layer included in thestretched laminate. The resulting product is an insolubilized stretchedlaminate 8″. The insolubilized stretched laminate 8″ is immersed in adyeing solution containing iodine and potassium iodide and having atemperature of 30° C. to form a dyed laminate 9 in which iodine isabsorbed in the insolubilized PVA layer. Then, the dyed laminate 9including the PVA layer with the absorbed iodine is immersed in thecross-linking boric acid aqueous solution 71 under a solutiontemperature of 40° C., for 60 seconds, to cross-link PVA molecules ofthe PVA layer with the absorbed iodine. The resulting product is across-linked dyed laminate 9′. The cross-linked dyed laminate 9′ isimmersed in an in-boric-acid-solution stretching bath 51 containingboric acid and potassium iodide and having a temperature of 75° C., for5 to 10 seconds, and then subjected to an in-boric-acid-solutionstretching based on an end-free uniaxial stretching process to attain astretching ratio of 3.3 to thereby form an optical film laminate 10.

As described above, based on the 2-stage stretching consisting of theelevated temperature in-air stretching and the in-boric-acid-solutionstretching, and the pre-treatments consisting of the insolubilizationbefore immersion in the dyeing bath and the cross-linking before thein-boric-acid-solution stretching, the process in the Example 4 makes itpossible to stably form an optical film laminate 10 including a 3μm-thick PVA layer making up a polarizing film in which PVA molecules ina PVA layer 2 formed on a non-crystallizable PET substrate 1 are highlyoriented, and iodine reliably absorbed in the PVA molecules throughdyeing is highly oriented in one direction in the form of an polyiodideion complex.

(Cleaning Step (G))

The dyed laminate 9 or the cross-linked dyed laminate 9′ in the Example1 or 4 is subjected to a stretching in the in-boric-acid-solutionstretching step (D), and then taken out of the boric acid aqueoussolution 51. Preferably, the taken-out optical film 10 including thepolarizing film 3 is directly fed to a cleaning step (G). The cleaningstep (G) is intended to wash out unnecessary residuals adhered on asurface of the polarizing film 3. Alternatively, the cleaning step (G)may be omitted, and the optical film 10 including the polarizing film 3may be directly fed to a drying step (H). However, if the cleaning is insufficient, boric acid is likely to precipitate from the polarizing film3 after drying of the optical film laminate 10. Specifically, theoptical film laminate 10 is fed to a cleaning apparatus 80 and immersedin a cleaning solution 81 containing potassium iodide having atemperature of 30° C., for 1 to 10 seconds, so as to prevent dissolutionof PVA of the polarizing film 3. A potassium iodide concentration of thecleaning solution 81 may be in the range of about 0.5 to 10 weight %.

(Drying Step (H))

The cleaned optical film laminate 10 is fed to a drying step (H) anddried therein. Then, the dried optical film laminate 10 is wound on atake-up unit 91 provided in side-by-side relation to the dryingapparatus 90, as a continuous web of an optical film laminate 10, toform a roll of the optical film laminate 10 including the polarizingfilm 3. Any appropriate process, such as natural drying, blow drying andthermal drying, may be employed as the drying step (H). In each of theExamples 1 and 4, the drying was performed by warm air at 60° C., for240 seconds in an oven type drying apparatus 90.

(Lamination and Transfer Step (I))

As mentioned above, the present invention is intended to provide amethod of producing a roll of an optical film laminate using apolarizing film comprising a polyvinyl alcohol type resin having amolecularly oriented dichroic material, wherein the polarizing film isformed to have optical characteristics satisfying the aforementionedrequired conditions, through a 2-stage stretching consisting of apreliminary in-air stretching and an in-boric-acid-solution stretching.

In order to form this optical film laminate, an optical film laminate 10including a polarizing film having a thickness of 10 μm or less (e.g.,the above 3 μm-thick polarizing film 3) and formed on anon-crystallizable PET substrate such as a non-crystallizable PETsubstrate, is subjected to a defect inspection, and then wound into aroll to form a roll of the optical film laminate 10. For example, a rollof an optical film laminate to be formed by the method of the presentinvention is used in a lamination/transfer step (I) illustrated in FIG.10. In the lamination/transfer step (I), the optical film laminate 10 isunrolled from the roll, and may be simultaneously subjected to alamination operation and a transfer operation, in the following manner.

The polarizing film 3 to be produced has a thickness of 10 μm, typicallyonly about 2 to 5 μm through the stretching which reduces the thickness.Thus, it is difficult to handle such a thin polarizing film 3 in theform of a single-layer. For this reason, the polarizing film 3 ishandled, for example, in the form of an optical film laminate 10, i.e.,under a condition that it is left on the non-crystallizable PETsubstrate, or, in the form of an optically functional film laminate 11obtained by laminating or transferring the polarizing film to anotheroptically functional film 4.

In the lamination/transfer step (I) illustrated in FIGS. 9 and 10, thepolarizing film 3 included in the continuous web of optical filmlaminate 10, and a separately prepared optically functional film 4 arelaminated together and taken up into a roll. In this take-up step, theoptically functional film laminate 11 is formed by transferring thepolarizing film 3 to the optically functional film 4 while peeling thenon-crystallizable PET substrate from the polarizing film 3.Specifically, the optical film laminate 10 is unrolled from the roll byan unrolling/laminating unit 101 included in a laminating/transferringapparatus 100, and the polarizing film 3 of the unrolled optical filmlaminate 10 is transferred to the optically functional film 4 by ataking-up/transferring unit 102. In the course of this operation, thepolarizing film 3 is peeled from the substrate 1, and formed as theoptically functional film laminate 11.

The optical film laminate 10 taken up into a roll by the take-up unit 91in the drying step (H) or the optically functional film laminate 11formed in the lamination/transfer step (I) may tale various otherstructures or mechanisms.

[Optical Characters of Polarizing Films Produced Under VariousConditions] (1) Improvement in Optical Characteristics of PolarizingFilm by Insolubilization (Examples 1 to 4)

As already described with reference to FIG. 8, each of the polarizingfilms produced based on the Examples 1 to 4 can overcome theaforementioned technical problems. The optical characteristics thereofcan satisfy the required performance for an optical display device of aliquid-crystal television using a large-sized display element. Further,as is clear from FIG. 8, the optical characteristics of thenon-insolubilized polarizing films in the Example 1 are inferior to theoptical characteristics of any polarizing film in the Examples 2 to 4subjected to the first and/or second insolubilizations. Comparingrespective optical characteristics of the Examples, a level of theoptical characteristics becomes higher in the following order: (Example1)<(Example 3 including only the first insolubilization)<(Example 2including only the second insolubilization)<(Example 4 including thefirst and second insolubilizations). A polarizing film produced by aproduction process comprising the first and/or second insolubilizationsteps, in addition to the production process for the optical filmlaminate 10 including the polarizing film 3, can be significantlyimproved in optical characteristic.

(2) Impact of Thickness of PVA Type Resin Layer on OpticalCharacteristics of Polarizing Film (Example 5)

In the Example 4, the 3 μm-thick polarizing film was formed bystretching the 7 μm-thick PVA layer. On the other hand, in the Example5, the 12 μm-thick PVA layer was first formed, and the 5 μm-thickpolarizing film was formed by stretching this PVA layer. The remainingconditions for producing these polarizing films was the same.

(3) Impact of Difference in Material of Non-Crystallizable PET Substrateon Optical Characteristics of Polarizing Film (Example 6)

In the Example 4, a non-crystallizable PET substrate copolymerized withisophthalic acid was used, whereas, in the Example 6, anon-crystallizable PET substrate copolymerized with1,4-cyclohexanedimethanol as a modifier group was used. In the Example6, a polarizing film was produced under the same conditions as those inthe Example 4, except the above difference.

Referring to FIG. 13, it shows that there is no significant differencein optical characteristics between respective ones of the polarizingfilms produced based on the Examples 4 to 6. This would be consideredthat the thickness of the PVA type resin layer and the type of thenon-crystallizable ester type thermoplastic resin do not have anyrecognizable impact on the optical characteristics.

(4) Improvement in Optical Characteristics of Polarizing Film byStretching Ratio during Preliminary In-Air (Examples 7 to 9)

In the Example 4, the stretching ratio during the first-stagepreliminary in-air stretching and the stretching ratio during thesecond-stage in-boric-acid-solution stretching were set to 1.8 and 3.3,respectively, whereas, in the Examples 7 to 9, the two stretching ratioswere set to 1.2 and 4.9 for the Example 7, 1.5 and 4.0 for the Example8, and 2.5 and 2.4 for the Example 9. In the Example 7 to 9, thepolarizing film was produced under the same conditions as those in theExample 4, except the above difference. For example, the stretchingtemperature during the preliminary in-air stretching was 130° C., andthe in-boric-acid-solution stretching was performed using a boric acidaqueous solution at a solution temperature of 75° C. The totalstretching ratio in each of the Examples 8 and 9 was 6.0 which issimilar to 5.94 as a total stretching ratio obtained when the stretchingratio during the preliminary in-air stretching in the Example 4 is setto 1.8. Differently, the total stretching ratio of the Example 7 waslimited to up to 5.88. This is because the stretching ratio during thein-boric-acid-solution stretching could be set to 4.9 or more, whichwould be caused by the attainable stretching ratio of non-crystallizablePET having an impact on the relationship between the stretching ratioduring the first-stage preliminary in-air stretching and the totalstretching ratio, as described based on FIG. 20.

Referring to FIG. 14, each of the polarizing films based on the Examples7 to 9 can overcome the technical problems concerning production of apolarizing film having a thickness of 10 μm or less and has opticalcharacteristics satisfying the required performance for optical displaydevices, as with the Example 4. Comparing respective optical propertiesof these Examples, a level of the optical properties becomes higher inthe following order: Example 7<Example 8<Example 4<Example 9. This showsthat, in cases where the stretching ratio during the first-stagepreliminary in-air stretching is set in the range of 1.2 to 2.5, even ifa final total stretching ratio after the second-stagein-boric-acid-solution stretching is set to a similar value, the opticalcharacteristics of the polarizing film become better as the stretchingratio during the first-stage preliminary in-air stretching is set to ahigher value. Thus, in a production process of an optical film laminate10 including a polarizing film 3, optical characteristics of the opticalfilm or the optical film laminate 10 including the polarizing film canbe further improved by setting the stretching ratio during thefirst-stage preliminary in-air stretching to a higher value.

(5) Improvement in Optical Characteristics of Polarizing Film byStretching Temperature during Preliminary In-Air Stretching (Examples 10to 12)

In the Example 4, the stretching temperature during the preliminaryin-air stretching was set to 130° C., whereas in the Examples 10 to 12,the stretching temperature during the preliminary in-air stretching wasset, respectively, to 95° C., 110° C., and 150° C., which are higherthan the glass transition temperature Tg of PVA. In these Examples, thepolarizing film was produced under the same conditions as those in theExample 4, except the above difference. For example, the stretchingratio during the preliminary in-air stretching was set to 1.8, and thestretching ratio during the in-boric-acid-solution stretching was set to3.3. The stretching temperature during the preliminary in-air stretchingin the Example 4 is 130° C. In these Examples including the Example 4,the production conditions are the same except that the stretchingtemperature is set to 95° C. for the Example 10, 110° C. for the Example11, 130° C. for the Example 4 and 150° C. for the Example 12.

Referring to FIG. 15, each of the polarizing films based on the Examples4 and 10 to 12 can overcome the technical problems concerning productionof a polarizing film having a thickness of 10 μm or less, and hasoptical characteristics satisfying the required performance for opticaldisplay devices. Comparing respective optical properties of theseExamples, a level of the optical properties becomes higher in thefollowing order: Example 10<Example 11<Example 4<Example 12. This showsthat, in cases where the stretching temperature during the first-stagepreliminary in-air stretching is set to a higher value than the glasstransition temperature, and gradually increased from 95° C. to 150° C.,even if a final total stretching ratio after the second-stagein-boric-acid-solution stretching is set to a similar value, the opticalcharacteristics of the polarizing film become better as the stretchingtemperature during the first-stage preliminary in-air stretching is setto a higher value. Thus, in a production process of an optical filmlaminate 10 including a polarizing film 3, optical characteristics ofthe optical film or the optical film laminate 10 including thepolarizing film can be further improved by setting the stretchingtemperature during the first-stage preliminary in-air stretching to ahigher value.

(6) Improvement of Optical Characteristics of Polarizing Film by TotalStretching Ratio (Examples 13 to 15)

In the Example 4, the stretching ratio during the first-stagepreliminary in-air stretching was 1.8, and the stretching ratio duringthe second-stage in-boric acid solution stretching was set to 3.3. Onthe other hand, in the Examples 13 to 15, only the stretching ratio inthe second-stage in-boric acid solution stretching was changed to 2.1,3.1 and 3.6, respectively. This means that the total stretching ratiosin the Examples 13 to 15 are 5.04 (about 5.0), 5.58 (about 5.5) and 6.48(about 6.5), respectively. The total stretching ratio in the Example 4is 5.94 (about 6). In these Examples including the Example 4, theproduction conditions are the same except that the total stretchingratio is set to 5.0 for the Example 13, 5.5 for the Example 14, 6.0 forthe Example 4 and 6.5 for the Example 15.

Referring to FIG. 16, each of the polarizing films based on the Examples4 and 13 to 15 can overcome the technical problems concerning productionof a polarizing film having a thickness of 10 μm or less and has opticalcharacteristics satisfying the required performance for liquid-crystaldisplay devices. Comparing respective optical properties of theseExamples, a level of the optical properties becomes higher in thefollowing order: Example 13<Example 14<Example 4<Example 15. This showsthat, in cases where the stretching ratio during the first-stagepreliminary in-air stretching is fixedly set to 1.8, and only thestretching ratio during the second-stage in-boric-acid-solutionstretching is variably set to allow the total stretching ratio to begradually increased to 5.0, 5.5, 6.0 and 6.5, the opticalcharacteristics of the polarizing film being better with the final totalstretching ratio having a higher value. Thus, in the production processof an optical film laminate 10 including a polarizing film 3, opticalcharacteristics of the optical film or the optical film laminate 10including the polarizing film can be further improved by setting thetotal stretching ratio during the first-stage preliminary in-airstretching and the second-stage in-boric-acid-solution stretching to ahigher value.

(7) Improvement of Optical Characteristics of Polarizing Film by TotalStretching Ratio in End-fixed Uniaxial Stretching (Examples 16 to 18)

In the Examples 16 to 18, optical film laminates were produced under thesame conditions as those in the Example 4, except the followingdifference. The difference is a stretching scheme in the preliminaryin-air stretching. In the example 4, an end-free uniaxial stretchingprocess is employed, whereas in each of the Examples 16 to 18, anend-fixed uniaxial stretching process is employed. In each of theseExamples, the stretching ratio during the first-stage preliminary in-airstretching was fixedly 1.8, and only the stretching ratio during thesecond-stage in-boric-acid-solution stretching was changed to 3.3, 3.9,4.4, respectively. This means that the total stretching ratio was 5.94(about 6.0) for the Example 16, 7.02 (about 7.0) for the Example 17 and7.92 (about 8.0) for the Example 18, respectively. In the Examples 16 to18, the production conditions are the same except the above difference.

Referring to FIG. 17, each of the polarizing films in accordance withthe Examples 16 to 18 can overcome the technical problems concerningproduction of a polarizing film having a thickness of 10 μm or less andhas optical characteristics satisfying the required performance foroptical display devices. Comparing respective optical properties ofthese Examples, a level of the optical properties becomes higher in thefollowing order: Example 16<Example 17<Example 18. This shows that, incases where the stretching ratio during the first-stage preliminaryin-air stretching is fixedly set to 1.8, and only the stretching ratioduring the second-stage in-boric-acid-solution stretching is variablyset to allow the total stretching ratio to be gradually increased to6.0, 7.0 and 8.0, the optical characteristics of the polarizing filmbeing better with the final total stretching ratio having a highervalue. Thus, in a production process of the optical film laminate 10including the polarizing film 3, optical characteristics of the opticalfilm or the optical film laminate 10 including the polarizing film canbe further improved by setting the total stretching ratio during thefirst-stage preliminary in-air stretching based on an end-fixed uniaxialstretching process and the second-stage in-boric-acid- solutionstretching to a higher value. It was also ascertained that, in caseswhere an end-fixed uniaxial stretching process is used in thefirst-stage preliminary in-air stretching, the final total stretchingratio can be increased as compared to cases where an end-free uniaxialstretching process is used in the first-stage preliminary in-airstretching.

Comparative Example 3

In the comparative example 3, under the same conditions as those in thecomparative example 1, a PVA aqueous solution was applied on a 200μm-thick PET substrate and dried to form a laminate including a 7μm-thick PVA layer formed on the PET substrate. Then, the laminate wasimmersed in a dyeing solution containing iodine and potassium iodide andhaving a temperature of 30° C. to form a dyed laminate including a PVAlayer having iodine absorbed therein. Specifically, the dyed laminate isformed by immersing the laminate in a dyeing solution containing 0.30 wt% of iodine and 2.1 wt % of potassium iodide at a solution temperatureof 30° C., for an arbitrary time, to allow the PVA layer making up atarget polarizing film (to be finally obtained) to have a single layertransmittance of 40 to 44%. Then, the dyed laminate including the PVAlayer having the absorbed iodine was subjected to anin-boric-acid-solution stretching at a stretching temperature of 60° C.based on an end-free uniaxial stretching process to attain a stretchingratio of 5.0. In this manner, various optical film laminates eachincluding a 3 μm-thick PVA layer integrally stretched with the PET resinsubstrate were formed.

(Reference Sample 1)

In the reference sample 1, a continuous web of a crystallizablepolyethylene terephthalate (hereinafter referred to as “crystallizablePET”) was used as a resin substrate, and a PVA aqueous solution wasapplied on a 200 μm-thick crystallizable PET substrate and dried to forma laminate including a 7 μm-thick PVA layer formed on the crystallizablePET substrate. A glass transition temperature of the crystallizable PETis 80° C. Then, the formed laminate was subjected to elevatedtemperature in-air stretching at a stretching temperature of 110° C.based on an end-free uniaxial stretching process to attain a stretchingratio of 4.0 to thereby form a stretched laminate. Through thestretching, the PVA layer included in the stretched laminate was changedinto a 3.3 μm-thick PVA layer having oriented PVA molecules. In thereference sample 1, the laminate could not be stretched at a stretchingratio of 4.0 or more in the elevated temperature in-air stretching at astretching temperature of 110° C.

In a subsequent dyeing step, the stretched laminate was formed as a dyedlaminate in which iodine is absorbed in the 3.3 μm-thick PVA layerhaving oriented PVA molecules. Specifically, the dyed laminate wasformed by immersing the stretched laminate in a dyeing solutioncontaining iodine and potassium iodide and having a temperature of 30°C., for an arbitrary time to cause iodine to be absorbed in the PVAlayer included in the stretched laminate, so as to allow the PVA layermaking up a target polarizing film to have a single layer transmittanceof 40 to 44%. An amount of iodine to be absorbed in the PVA layer havingoriented PVA molecules was adjusted to produce various dyed laminatesdifferent in single layer transmittance and polarization rate. Then, theformed dyed laminate was subjected to cross-linking. Specifically, thedyed laminate was cross-linked by immersing it in a cross-linking boricacid aqueous solution containing 3 weight parts of boric acid withrespect to 100 weight parts of water and 3 weight parts of potassiumiodide with respect to 100 weight parts of water, at a solutiontemperature of 40° C. for 60 seconds. The cross-linked dyed laminate inthe comparative example 1 corresponds to the optical film laminate inthe Example 4. Thus, cleaning, drying and lamination and/or transfersteps in the comparative example 1 are the same as those in the Example4.

(Reference Sample 2)

In the reference sample 2, a crystallizable PET was used as a resinsubstrate, and a laminate including a 7 μm-thick PVA layer formed on thecrystallizable PET substrate was formed in the same manner as that inthe reference sample 1. Then, the formed laminate was subjected toelevated temperature in-air stretching at a stretching temperature of100° C. based on an end-free uniaxial stretching process to attain astretching ratio of 4.5 to thereby form a stretched laminate. Throughthe stretching, the PVA layer included in the laminate was changed intoa 3.3 μm-thick PVA layer having oriented PVA molecules. In the referencesample 2, the laminate could not be stretched at a stretching ratio of4.5 or more in the elevated temperature in-air stretching at astretching temperature of 100° C.

Then, a dyed laminate was formed from the stretched laminate. The dyedlaminate was formed by immersing the stretched laminate in a dyeingsolution containing iodine and potassium iodide and having a temperatureof 30° C., for an arbitrary time to cause iodine to be absorbed in thePVA layer included in the stretched laminate, so as to allow the PVAlayer making up a target polarizing film to have a single layertransmittance of 40 to 44%. In the reference sample 2, an amount ofiodine to be absorbed in the PVA layer having oriented PVA molecules wasadjusted to produce various dyed laminates different in single layertransmittance and polarization rate, as with the reference sample 1.

(Reference Sample 3)

In the reference sample 3, a crystallizable PET was used as a resinsubstrate, and a laminate including a 7 μm-thick PVA layer formed on thecrystallizable PET substrate was formed in the same manner as that inthe reference sample 1 or 2. Then, the formed laminate was immersed in adyeing solution containing iodine and potassium iodide and having atemperature of 30° C., for an arbitrary time to cause iodine to beabsorbed in the PVA layer included in the laminate, so as to allow thePVA layer making up a target polarizing film to have a single layertransmittance of 40 to 44%, to form various dyed laminates eachincluding the PVA layer having iodine absorbed therein. Subsequently,the formed dyed laminate was subjected to elevated temperature in-airstretching at a stretching temperature of 90° C. based on an end-freeuniaxial stretching process to attain a stretching ratio of 4.5 tothereby form a stretched laminate. Through the stretching, the PVA layerincluded in the stretched laminate was changed into a 3.3 μm-thick PVAlayer having oriented PVA molecules. In the reference sample 3, thelaminate could not be stretched at a stretching ratio of 4.5 or more inthe elevated temperature in-air stretching at a stretching temperatureof 90° C.

[Measurement Method]

(Thickness Measurement)

A thickness of each of the non-crystallizable PET substrate, thecrystallizable PET substrate and the PVA layer was measured using adigital micrometer (KC-351C from Anritsu Electric Co., Ltd.).

(Measurement of Transmittance and Polarization Rate)

Each of the single layer transmittance T, the parallel transmittance Tpand the cross transmittance Tc of the polarizing film was measured usinga UV-visible spectrophotometer (V7100 from JASCO Corporation). Eachvalue of T, Tp and Tc is presented by a Y value measured according toJIS Z8701 (visual field of 2 degrees, C light source) and corrected forspectral luminous efficacy.

The polarization rate P was calculated in accordance with the followingformula using the above transmittance.

Polarization rate P={(Tp−Tc)/(Tp+Tc)}^(1/2)×100

(Evaluation of Orientation Function of PET)

A Fourier Transform Infrared Spectrometer (FT-IR) (SPECTRUM 2000 fromPerkinElmer, Inc.) was used as the measurement device. Attenuated totalreflection (ATR) of polarizing light was measured to evaluate thesurface of a PET resin layer. The orientation function was calculated inthe following manner. Measurements were made on the polarizing light inthe directions of 0° and 90° with respect to the stretching direction.Absorption intensity of the obtained spectral at 1340 cm⁻¹ was used tocalculate the orientation function according to the Formula 4 (see theNon-Patent Document 1) described below. The condition of f=1 indicates acomplete or perfect orientation, whereas the condition f=0 indicates arandom orientation. The peak observed at 1340 cm⁻¹ is considered asindicating the absorption induced by a methylene in an ethylene glycolunit of PET.

$\begin{matrix}\begin{matrix}{f = {\left( {{3{\langle{\cos^{2}\theta}\rangle}} - 1} \right)/2}} \\{= {\left\lbrack {\left( {R - 1} \right)\left( {R_{0} + 2} \right)} \right\rbrack/\left\lbrack {\left( {R + 2} \right)\left( {R_{0} - 1} \right)} \right\rbrack}} \\{= {\left( {1 - D} \right)/\left\lbrack {c\left( {{2D} + 1} \right)} \right\rbrack}} \\{= {{- 2} \times {\left( {1 - D} \right)/\left( {{2D} + 1} \right)}}}\end{matrix} & \left( {{Formula}\mspace{14mu} 4} \right)\end{matrix}$

where: c=(3 cos²β−1)/2;

β=90°, an angle of transition dipole moment with respect to an axis ofmolecular chain;

θ: an angle of molecular chain with respect to the stretching direction;

R ₀=2 cot²β;

1/R=D=(I⊥)/(I//) (A value of D becomes larger as PET is more highlymolecularly oriented);

I⊥=absorption intensity measured when polarizing light is entered in adirection perpendicular to the stretching direction; and

I//=absorption intensity measured when polarizing light is entered in adirection parallel to the stretching direction.

(Evaluation of Orientation Function of PVA)

A Fourier Transform Infrared Spectrometer (FT-IR) (SPECTRUM 2000 fromPerkinElmer, Inc.) was used as the measurement device. Attenuated totalreflection (ATR) of polarizing light was measured to evaluate thesurface of the PVA resin layer. The orientation function was calculatedin the following manner. Measurements were made on the polarizing lightin the directions of 0° and 90° with respect to the stretchingdirection. Absorption Intensity of the obtained spectral at 2941 cm⁻¹was used to calculate the orientation function according to the aboveFormula 4. Intensity at 3330 cm⁻¹ was used as a reference peak,intensity at 2941 cm⁻¹/intensity at 3330 cm⁻¹ was calculated as theintensity I. The condition of f=1 indicates the complete or perfectorientation, whereas the condition f=0 indicates a random orientation.The peak observed at 2941 cm⁻¹ is considered to be absorption induced byvibration of the main chain of PVA (—CH₂—).

(Evaluation of Crystallization Degree of PVA)

A Fourier Transform Infrared Spectrometer (FT-IR) (SPECTRUM 2000 fromPerkinElmer, Inc.) was used as the measurement device. Attenuated totalreflection (ATR) of polarizing light was measured to evaluate thesurface of the PVA resin layer. The crystallization degree wascalculated in the following manner. Measurements were made on thepolarizing light in the directions of 0° and 90° with respect to thestretching direction. Intensities of the obtained spectral at 1141 cm⁻¹and at 1440 cm⁻¹ were used to calculate the crystallization degree. Itwas preliminarily ascertained that a level of the intensity at 1141 cm⁻¹is correlated with an amount of crystal, and calculations were madeusing the intensity at 1440 cm⁻¹ as a reference peak to determine acrystallization index with the following equation (Formula 6). Further,a sample of PVA having a known crystallization degree was used to createa crystallization index and a calibration curve in advance, and thecalibration curve was used to calculate the crystallization decree fromthe crystallization index (Formula 5).

Crystallization degree=63.8×(crystallization index)−44.8   (Formula 5)

Crystallization index=((I (1141 cm⁻¹) 0°+2×I (1141 cm⁻¹))90°)/3)/((I(1440 cm⁻¹) 0°+2×I (1440 cm⁻¹))90°/3)   (Formula 6)

where: I (1141 cm⁻¹) 0°=intensity at 1141 cm⁻¹ when polarizing light isentered in a direction parallel to the stretching direction;

I (1141 cm⁻¹) 90°=intensity at 1141 cm⁻¹ when polarizing light isentered in a direction perpendicular to the stretching direction;

I (1440 cm⁻¹) 0°=intensity at 1440 cm⁻¹ when polarizing light is enteredin a direction parallel to the stretching direction; and

I (1440 cm⁻¹) 90°=intensity at 1440 cm⁻¹ when polarizing light isentered in a direction perpendicular to the stretching direction.

[Example of Optical Display Device]

FIGS. 11 a, 11 b and 12 illustrate examples of optical display deviceseach using the above polarizing film according to the present invention.

FIG. 11 a is a sectional view illustrating one example of a fundamentalstructure of an organic EL display device. This display device 200comprises an optical display panel 201 in the form of an organic ELdisplay panel, and a polarizing film 203 joined to one surface of thedisplay panel 201 through an optically transparent adhesive layer 202. A¼ wavelength phase difference film 204 is bonded to an outer surface ofthe polarizing film 203. Optionally, a transparent window 205 asindicated by the dotted line may be disposed on an outer side of the ¼wavelength phase difference film 204. This structure is useful when apolarized sunglass is used.

FIG. 11 b is a sectional view illustrating another example of thestructure of the organic EL display device. This display device 200 acomprises an optical display panel 201 a in the form of an organic ELdisplay panel, and a ¼ wavelength phase difference film 204 a joined toone surface of the display panel 201 a through an optically transparentadhesive layer 202 a. A polarizing film 203 a is bonded to an outersurface of the ¼ wavelength phase difference film 204 a. Further, aprotective layer 206 is bonded to an outer surface of the polarizingfilm 203 a. Optionally, a transparent window 205 a as indicated by thedotted line may be disposed on an outer side of the protective layer206, i.e., on a viewing side of the optical display device 200 a. Inthis example, outside light is converted to linearly-polarized lightthrough the polarizing film 203 a and further converted tocircularly-polarized light through the 1/4 wavelength phase differencefilm 204 a. This structure is capable of blocking outside light fromreturning to the viewing side of the optical display device due toreflection by the surface of the optical display panel 201 a, etc., andeffective to prevent internal reflection of outside light.

As a material for joining or bonding together layers, or films, it ispossible to use, as a base polymer, at least one appropriately selectedfrom the group consisting of acrylic-based polymer, silicone-basedpolymer, polyester, polyurethane, polyamide, polyether, fluorine orrubber-based polymer, isocyanate-based polymer, polyvinyl alcohol-basedpolymer, gelatin-based polymer, vinyl or latex-based polymer, andwaterborne polyester.

As mentioned above, the polarizing film 203 is formed to have athickness of 10 μm or less, and satisfy the aforementioned opticalcharacteristics. This polarizing film 203 is extremely thin as comparedto polarizing films used in this type of conventional optical displaydevice, so that stress arising from expansion/contraction occurringdepending on conditions of temperature or humidity becomes significantlysmaller. Thus, it becomes possible to considerably reduce a risk thatstress arising from expansion/contraction of the polarizing film causesdeformation, such as warp, in the display panel 201 adjacent thereto,and drastically suppress deterioration in quality of display due to thedeformation. In this structure, as the adhesive layer 202, a materialhaving a diffusing function may be used, or a two-layer structure of anadhesive layer and a diffusion layer may be employed.

As a material for improving adhesion force of the adhesive layer 202, ananchor layer as disclosed, for example, in JP 2002-258269A (PatentDocument 6), JP 2004-078143A (Patent Document 7) and JP 2007-171892A(Patent Document 8), may be provided. A binder resin is not limited to aparticular type, as long as it is capable of improving anchoring forceof the adhesive layer. Specifically, it is possible to use resin(polymer) having an organic reactive group, such as epoxy-based resins,polyurethane-based resins, polyester-based resins, polymers including anamino group in molecules, ester urethane-based resins, or acrylic-basedresins including an oxazoline group.

Further, an antistatic agent as disclosed, for example, in JP2004-338379A (Patent Document 9) may be added to the anchor layer toprovide an antistatic capability thereto. The antistatic agent forproviding an antistatic capability may includes an ionicsurfactant-based material, a conductive polymer-based material such aspolyaniline, polythiophene, polypyrrole or polyquinoxaline, and a metaloxide-based material such as tin oxide, antimony oxide or indium oxide.Particularly in view of optical characteristics, appearance, antistaticeffect and stability of antistatic effects during heating orhumidification, it is preferable to use the conductive polymer-basedmaterial. Among the conductive polymer-based materials, it isparticularly preferable to use a water-soluble conductive polymer suchas polyaniline or polythiophene, or a water-dispersible conductivepolymer. When the water-soluble conductive polymer or thewater-dispersible conductive polymer is used as a material for formingan antistatic layer, it becomes possible to suppress transformation ofan optical film substrate due to an organic solvent during coating.

FIG. 12 illustrates an example of an optical display device 300 having atransmissive type liquid-crystal display panel 301 as an optical displaypanel. In the optical display device 300, a first polarizing film 303 isjoined to a viewing-side surface of the liquid-crystal display panel 301through a first adhesive layer 302, and a protective layer 304 is joinedto the first polarizing film 303 through a bonding-facilitating layer307. A 1/4 wavelength phase difference film 309 is joined to theprotective layer 304. Optionally, an antistatic layer 308 may be formedon the ¼ wavelength phase difference film 309. Optionally, a window 305may also be disposed on an outer side of the ¼ wavelength phasedifference film 309. A second polarizing film 303 a is placed on theother surface of the liquid-crystal display panel 301 through a secondadhesive layer 302 a. As is commonly known in the field of transmissiveliquid-crystal display devices, a backlight 310 is disposed on a backside of the second polarizing film 303 a.

Embodiments

The present invention will be specifically described in accordance witha first embodiment taking reference to FIG. 30. A thermoplastic resinsubstrate 1 made of non-crystallizable PET, for example, is fed out ofthe stretching apparatus after having been subjected to film formationby the laminate forming apparatus 20, preliminary in-air stretching inthe oven 33, dyeing with a dichroic pigment in the dyeing apparatus 40and in-boric-acid-solution stretching in the boric acid aqueous solutionbath 52, as illustrated in FIGS. 9 and 10, so as to be an optical filmlaminate 400 in which a polarizing film 3 having a thickness of 10 μm orless, specifically, 3 to 4 μm, is formed on the substrate 1. At thisstage, the optical film laminate 400 may be wound into a roll once, ormay be fed to a next step or station directly and continuously. Anoptical film laminate forming apparatus illustrated in FIG. 30, which isto be used in the next step, has a separator film attaching station 500,and a defect inspection station 600.

The separator film attaching station 500 is equipped with a pair ofattaching rollers 501, 502. In the separator film attaching station 500,the optical film laminate 400 is fed between the attaching rollers 501,502, in a posture where the polarizing film 3 faces downwardly. Aseparator film 503 is unrolled from a roll 503 a of the separator film503, and fed between the attaching rollers 501, 502 in such a mannerthat it is superimposed on a lower surface of the optical film laminate400. Just before the optical film laminate 400 and the separator film503 are entered between the attaching rollers 501, 502, an adhesive 504a is supplied between the optical film laminate 400 and the separatorfilm 503 to form a layer. Thus, when the optical film laminate 400 andthe separator film 503 are fed out of the attaching rollers 501, 502, aseparator-attached optical film laminate 510 is formed in which theseparator film 503 is attached to a surface of the polarizing film ofthe optical film laminate 400 through an adhesive layer 504. At thisstage, the separator-attached optical film laminate 510 may be woundinto a roll once. A surface of the separator film 503 facing theadhesive layer 504 is preliminarily subjected to a releasing treatmentto allow an adhesion force of the separator film 503 with respect to theadhesive layer 504 to become weaker than an adhesion force between thepolarizing film 3 and the adhesive layer 504. Thus, as explained below,when the separator film 503 is peeled from the optical film laminate400, the adhesive layer 504 will be left on the side of the optical filmlaminate 400. This adhesive layer 504 will be used as bonding means whenthe optical film laminate 400 is attached to another member such as adisplay panel.

The defect inspection station 600 is equipped with reference-pointprinting means 610 for printing a reference mark M on a surface of thesubstrate 1 of the separator-attached optical film laminate 510. Thereference-point printing means 610 is designed to create a mark servingas a positional reference in a lengthwise direction of theseparator-attached optical film laminate 510, onto theseparator-attached optical film laminate 510 at an appropriate positionadjacent to a leading edge thereof in a feed direction.

In the first embodiment illustrated in FIG. 30, the separator-attachedoptical film laminate 510 fed out of the attaching rollers 501, 502 isdirectly fed to pass through the reference point printing means 610. Afeed-amount measuring means composed of a length measuring roller 611 isdisposed downstream of the printing means 610. The length measuringroller 611 is adapted to measure a feed amount of the separator-attachedoptical film laminate fed through the roller 611, based on a rotationalamount thereof, and send a measurement signal to laminate-feed-amountcalculation means 620 a of a storage/calculation unit 620 provided inthe optical film laminate forming apparatus.

The defect inspection station 600 is equipped with a separator-filmpeeling section 601 on a downstream side with respect to the lengthmeasuring roller 611 in the feed direction. The separator-film peelingsection 601 comprises a pair of guide rollers 602, 603, a peeled-filmguide roller 604 for guiding the separator film 503 in a state afterbeing peeled or under a condition that the separater film 503 has beenpeeled away, and a take-up roller 605 for taking up the peeled separatorfilm 503. The optical film laminate 400 from which the separator film503 has been peeled, has a structure in which the adhesive layer 504 isleft on the surface of the polarizing film 3. The optical film laminate400 having the adhesive layer 504 is fed to a defect inspection section630. The defect inspection section 630 comprises reference-point readingmeans 631, and transmitted-light detection type optical-defect detectionmeans composed of a light source 632 and a light sensing element 633. Aread signal from the reference-point reading means 631 is sent toreference-point-read-time storage means 620 b of the storage/calculationunit 620, and the reference-point-read-time storage means 620 b isoperable to store a clock time when the reference point is detected. Adefect detection signal from the optical-defect detection means is sentto defect-detection-time calculation means 620 c of thestorage/calculation unit 620, and the defect-detection-time calculationmeans 620 c is operable to calculate a clock time when the defect isdetected and store the calculated clock time. Respective signals fromthe laminate-feed-amount calculation means 620 a, thereference-point-read-time storage means 620 b and thedefect-detection-time calculation means 620 c are input into adefect-position calculation section 672 of a control unit 670 providedin the optical film laminate forming apparatus. The defect-positioncalculation section 672 is operable, in response to receiving the inputof the above signals, to calculate a defect position as measured fromthe reference mark M, and send a signal indicative of the defectposition to a defect-mark-printing-instruction generation section 620 dof the storage/calculation unit 620.

After passing through the defect inspection station 600, the opticalfilm laminate 400 is fed to pass through a separator film re-attachingstation 640. The separator film re-attaching station 640 is equippedwith a pair of re-attaching rollers 641, 642 for re-attaching aseparator film 503 unrolled from a roll 503 a of the separator film 503,to the optical film laminate 400 through the adhesive layer 504 left onthe polarizing film 3 of the optical film laminate 400. The optical filmlaminate 400 fed out of the re-attaching rollers 641, 642 is formed as aseparator-attached optical film laminate 510 in which the separator film503 is attached to the optical film laminate 400. The separator filmpeeled through the separator-film peeling section 601may be used as theseparator film 503 to be re-attached to the optical film laminate 400.Alternatively, a separately prepared separator film may also be used.

The separator-attached optical film laminate 510 fed out of there-attaching rollers 641, 642 is fed to pass through a second defectinspection station 650 which may be optionally provided. The seconddefect inspection station 650 is equipped with a reference-pointdetection means 651, and optical-defect detection means 652. Theoptical-defect detection means 652 comprises a light source 652 a foremitting light to a surface of the separator film 503 of theseparator-attached optical film laminate 510, and a light-receivingelement 652 b for receiving reflected light from the surface of theseparator film 503. The optical-defect detection means 652 is operableto detect a surface defect of the separator film 503 of theseparator-attached optical film laminate 510. A detection signal fromthe reference-point detection means 651 is sent to thereference-point-read-time storage means 620 b, and a detection signalfrom the light-receiving element 652 b is sent to thedefect-detection-time calculation means 620 c.

The separator-attached optical film laminate 510 passing through thesecond defect inspection station 650 is fed to pass through feed-amountmeasuring means having a length measuring roller 660, and thefeed-amount measuring means is operable to measure a feed amount of thelaminate 510. A signal indicative of the measured feed amount is sent toa reference-point cross-checking section 671 of the control unit 670provided in the optical film laminate forming apparatus. Reference-pointreading means 661 is provided downstream of the length measuring roller660. The reference-point reading means 661 is operable to read thereference mark M formed on the optical film laminate 400, and send asignal indicative of information about a clock time when the mark Mpasses therethrough, to the reference-point cross-checking section 671.The reference-point cross-checking section 671 is operable, in responseto receiving the signals from the length measuring roller 660 and thereference-point reading means 661, to input a signal indicative of alaminate feed amount as measured from the reference mark M, to thedefect-mark-printing-instruction generation section 620 d of thestorage/calculation unit 620. The defect-mark-printing-instructiongeneration section 620 d is operable, based on the defect positionsignal from the defect-position calculation section 672, and the feedamount signal from the reference-point cross-checking section 671, togenerate a printing instruction for printing a defect mark D at thedefect position on the separator-attached optical film laminate 510, andsend the instruction to a printing drive section 673. According to theprinting instruction, a mark printing unit 662 disposed downstream ofthe reference-point reading means 661 is activated to print the defectmark D at a position corresponding to the defect, on the thermoplasticresin substrate of the separator-attached optical film laminate 510. Theseparator-attached optical film laminate 510 with the printed mark istaken up to form a roll 680.

The first embodiment has been described based on an example in which thedefect position is printed on the laminate 510 in the form of the defectmark D. Alternatively, an identification mark for identifying each roll680 of the laminate 510 may be created on the roll, and a defectposition may be stored in the storage/calculation unit 620 inassociation with the identification mark for identifying each roll 680of the laminate 510. In this case, in a subsequent station using theroll 680 of the laminate 510, the defect position of the roll can beread from the storage/calculation unit 620 based on the identificationmark of the roll, to recognize the defect position of the optical filmlaminate.

FIG. 31 is a schematic diagram corresponding to FIG. 30, andillustrating a production process for a roll of an optical laminate,according to a second embodiment of the present invention. In FIG. 31, acomponent or element corresponding to that in the first embodimentillustrated in FIG. 30 is defined by the same reference numeral or code,and its description will be omitted. The second embodiment in FIG. 31 isdifferent from the first embodiment in FIG. 30 in that, before theseparator film 503 is joined to the polarizing film 3 of the opticalfilm laminate 400, an optically functional film 800 is bonded to thesurface of the polarizing film 3 through a bonding agent 801. Theoptically functional film 800 may be a ¼ wavelength phase differencefilm, a viewing angle compensation film, or any other opticalcompensation film used in this technical field, as mentioned above. Thisoptically functional film 800 is unrolled from a roll 800 a, and fedthrough a guide roller 802. Then, it is bonded to the optical filmlaminate 400 by a pair of attaching rollers 803, 804, to form an opticalfilm intermediate laminate 510 a. Thus, in the second embodiment, theseparator film 503 is attached onto the optically functional film 800through the adhesive layer 504 to form an optical laminate 510 b. Aremaining part of the process in the second embodiment is the same asthat in the first embodiment illustrated in FIG. 30.

A third embodiment illustrated in FIG. 32 is different from the secondembodiment illustrated in FIG. 31 in that an optically functional film800 is bonded to the surface of the polarizing film 3 of the opticalfilm laminate 400 through a bonding agent 801, instead of joining theseparator film 503 to the side of the polarizing film 3. After theoptically functional film 800 is bonded to the polarizing film 3, thethermoplastic resin substrate 1 used for stretching is peeled from thepolarizing film 3 by a pair of peeling roller 810, 811, to form anoptical film intermediate laminate 510 c. The peeled substrate 1 istaken up into a roll 813 through a guide roller 812.

In the optical film intermediate laminate 510 c formed by peeling thesubstrate 1 from the optical film laminate 400, a mark M indicative of areference point is printed on a surface of the optically functional film800 by reference-point printing means 610. Then, the optical filmintermediate laminate 510 c is fed to a separator-film attaching station500A via a length measuring roller 611. In the separator film attachingstation 500A, a separator film 503 unrolled from a roll 503 a of theseparator film 503 is fed to be superimposed on a surface of the opticalfilm intermediate laminate 510 c from which the substrate 1 is peeled,so that it is attached to the polarizing film 3 by a pair of attachingrollers 501, 502, through an adhesive 504 a, to form an optical filmlaminate 510 d.

When the optical film laminate 510 d passes through a pair of peelingrollers 602, 603, the separator film 503 is peeled from the laminate 510d to form a laminate having a structure in which the adhesive layer 504a adheres to the polarizing film 3 of the optical film intermediatelaminate 510 c. Through a defect inspection station 630, this laminateis sent to a separator film re-attaching station 640. In this station640, a separator film 503 is joined to the laminate through the adhesivelayer 504 a on the surface of the polarizing film 3 of the laminate toform an optical film laminate 510 d. In the third embodiment, adefect-position storage section 620 e for storing a defect position asmeasured from a reference position is provided, in place of thedefect-mark-printing-instruction generation section 620 d of thestorage/calculation unit 620 in FIGS. 30 and 31. Information about thedefect position stored in the defect-position storage section 620 e isstored in an information storage medium 690 which is separate from acontrol unit 670. Identification information conversion means 673 aprovided in the control unit 670 is operable to activate aroll-identification-information printing means 662 a to print, on theoptically functional film 800 of the laminate 510 a, identificationinformation I for identifying the laminate 510 a . The informationstorage medium 690 is adapted to store the identification information inassociation with the defect position information. Thus, in a subsequentstation using a roll 680 of the optical film laminate 510 d, the defectposition of the roll 680 can be read from the information storage medium690. A remaining part of the process in the third embodiment illustratedin FIG. 32 is the same as that in the second embodiment illustrated inFIG. 31.

FIG. 33 is a schematic diagram corresponding to FIG. 32, andillustrating a fourth embodiment of the present invention. The fourthembodiment is different from the third embodiment in FIG. 32 in that,before the separator film 503 is attached to the surface of the laminatefrom which the substrate 1 is peeled, a second optically functional film850 is bonded to the surface of the polarizing film of the laminateafter peeling the substrate 1, through a bonding agent 851. The secondoptically functional film 850 is unrolled from a roll 850 a, and fedthrough a guide roller 852. Then, it is attached to the laminate 510 cby a pair of attaching rollers 803 a, 804 a, to form an optical filmintermediate laminate 510 e. Thus, in the fourth embodiment, theseparator film 503 is joined onto the second optically functional film850 through the adhesive layer 504 a to form an optical laminate 510f.Although a reference-point printing means 610 and a length measuringroller 611 are disposed downstream of the attaching rollers 501, 502,their functions are the same as those in the other embodiments.

Although the present invention has been described in term of specificexemplary embodiments, it is to be understood that various changes andmodifications will be apparent to those skilled in the art. Therefore,the present invention is not limited by the description contained hereinor by the drawings, but only by the appended claims and their legalequivalents.

EXPLANATION OF CODES

-   1: Substrate-   2: PVA type resin layer-   3: Polarizing film-   4: Optically functional film-   5: Second optically functional film-   7: PVA resin layer-including laminate-   8: Stretched laminate-   8′: Roll of stretched laminate-   8″: Insolubilized stretched laminate-   9: Dyed laminate-   9′: Cross-linked dyed laminate-   10: Optical film laminate-   11: Optically functional film laminate-   20: Laminate forming apparatus-   21: Coating means-   22: Drying means-   23: Surface modifying unit-   30: Preliminary in-air stretching apparatus-   31: Stretching means-   32: Take-up unit-   33: Oven-   40: Dyeing apparatus-   41: Dyeing solution-   42: Dyeing bath-   43: Feeding unit-   50: In-boric-acid- solution stretching apparatus-   51: Boric acid aqueous solution-   52: Boric acid aqueous solution bath-   53: Stretching means-   60: Insolubilization apparatus-   61: Insolubilizing boric acid aqueous solution-   70: Cross-linking apparatus-   71: Cross-linking boric acid aqueous solution-   80: Cleaning apparatus-   81: Cleaning solution-   90: Drying apparatus-   91: Take-up unit-   100: Lamination/transfer apparatus-   101: Unrolling/laminating apparatus-   102: Take-up/transfer apparatus-   (A): Laminate preparation step-   (B): Preliminary in-air stretching step-   (C): Dyeing step-   (D): In-boric-acid-solution stretching step-   (E): First insolubilization step-   (F): Cross-linking step including second insolubilization-   (G): Cleaning step-   (H): Drying step-   (I): Laminating/transfer process-   400: Optical film laminate-   500: Separator film attaching station-   600: Defect inspection station-   620: Storage/calculation unit-   670: Control unit-   680: Roll of optical film laminate

1. A method of producing a roll of an optical film laminate, comprisingthe steps: providing a roll of a separator film-attached optical filmlaminate which comprises a continuous web of an optical film laminateincluding a polarizing film which consists of a polyvinyl alcohol typeresin layer and has a thickness of 10 μm or less and an absorption axisin a lengthwise direction of the optical film laminate, and a separatorfilm attached to the optical film laminate through an adhesive layer,wherein the polarizing film is formed by performing an stretchingsub-step of subjecting a laminate comprising a continuous web of athermoplastic resin substrate and a polyvinyl alcohol type resin layerformed on the substrate, to a uniaxial stretching in a lengthwisedirection of the laminate to attain a stretching ratio of 5.0 to 8.5 tothereby reduce a thickness of the polyvinyl alcohol type resin layer to10 μm or less, and an absorption sub-step of causing a dichroic materialto be absorbed in the polyvinyl alcohol type resin layer, and anadhesion force of the separator film with respect to the adhesive layeris weaker than an adhesion force of the optical film laminate withrespect to the adhesive layer; peeling the separator film from theoptical film laminate in such a manner as to allow the adhesive layer toadhere to a side of the polarizing film, while unrolling the opticalfilm laminate from the roll and feeding the unrolled optical filmlaminate in the lengthwise direction; in a state after the separatorfilm is peeled, detecting a defect existing in the optical film laminateand the adhesive layer; upon detection of a defect in the continuous webof optical film laminate, recording a position of the defect; after thestep of detecting a defect, attaching a separator film to the adhesivelayer to form a separator film-attached optical film laminate; andwinding the formed separator film-attached optical film laminate into aroll.
 2. The method as defined in claim 1, which further comprises thestep of, based on the recorded positional information about the defect,printing a defect mark on the continuous web of optical film laminate ata position corresponding to the defect.
 3. The method as defined inclaim 1, wherein identification information for identifying the opticalfilm laminate having the defect is stored in an external storage devicein association with the recorded positional information about thedefect.
 4. The method as defined in any claim 1, wherein the separatorfilm in the separator film-attached optical film laminate is attached tothe optical film laminate on the side of the polarizing film.
 5. Themethod as defined in claim 4, wherein an optically functional film layeris disposed between the separator film and the polarizing film.
 6. Themethod as defined in claim 1, wherein the step of providing a roll of aseparator film-attached optical film laminate includes: bonding anoptically functional film to the continuous web of optical film laminateincluding the polarizing film, on the side of the polarizing film;peeling the substrate from the polarizing film; and attaching theseparator film to the laminate comprising the polarizing film and theoptically functional film, on the side of the polarizing film, throughan adhesive.
 7. The method as defined in claim 6, wherein, beforeattaching the separator film, a second optically functional film isbonded to the laminate comprising the polarizing film and the opticallyfunctional film, on the side of the polarizing film, and the separatorfilm is attached onto the second optically functional film through anadhesive.
 8. The method as defined in claim 1, wherein the stretching isa 2-stage stretching consisting of a preliminary in-air stretching andan in-boric-acid-solution stretching, and wherein the stretching isperformed to attain a total stretching ratio of 5.0 to 8.5.